My understanding of REST is simply that a resource needs some means of self-describing itself. My understanding is that this isn't specifically tied to any one protocol (i.e. HTTP) and that there are theoretically numerous ways of achieving this. This is based on an answer to a SO question here: SOAP vs REST (differences) (and unlike the terrible answer to this question: Are Relay and Graphql RESTful?)
Since a GraphQL API is self-describing via introspection, doesn't that mean that GraphQL is RESTful by default since a client can use introspection to figure out how to query it?
While GraphQL is often mentioned as the replacement for REST, both tackle different problems actually.
REST, to start with, is not a protocol but just a style, which, if applied correctly and fully, just decouples clients from servers. A server following the REST principals will therefore provide the client with any information needed to take further steps. A client initially starts without any a-priori knowledge and learns on the fly through issuing requests and processing responses. HATEOAS describes the interaction model a REST architectue should be build upon. It thereby states that a link should be used to request new information which drives its internal flow. On utilizing similar representation to Web forms (HTML) a server can teach a client on needed inputs. Through the affordance of the respective elements a client knows, without any need for external documentation, what to do. I.e. It might find a couple of options to chose one or multiple options from, enter or update some freetext or push some buttons. In HTML forms usually trigger a POST request and send the entered data as application/x-www-form-urlenceded to the server though the form element itself may define something different.
While REST is protocol agnostic, meaning it can be build up ontop of many protocols, HTTP is probably the most prominent one. A common sample for a RESTful client is the Web browser we are all to familiar with. It will start by invoking either a bookmarked URI or invoke one entered in the address bar and progress from there on.
HTTP doesn't specify the representation the request or response has to be sent in but leaves that to clients and servers negotiating them. This helps in decoupling as both client and servers can rely on the common interface (HTTP) and only bind strongly onto the known media types used to exchange data in. A peer not being able to process a document in a certain representation (due to the lack of the respective mime type support) will indicate his other peer via a respective HTTP status code that it does not understand, and therefore can't serve, the requested media-type format. The media type, which is just a human readable documentation of the syntax and the semantics of the data payload, is therefore the most important part in a REST architecture. Even Fielding claimed:
A REST API should spend almost all of its descriptive effort in defining the media type(s) used for representing resources and driving application state, or in defining extended relation names and/or hypertext-enabled mark-up for existing standard media types. Any effort spent describing what methods to use on what URIs of interest should be entirely defined within the scope of the processing rules for a media type (and, in most cases, already defined by existing media types). [Failure here implies that out-of-band information is driving interaction instead of hypertext.]
A media type teaches a peer how to parse and interpret the received payload and to actually make sense out of it, though plenty of people still confuse REST for a JSON based HTTP API with over-engineered URIs they put to much effort in to give the URI some kind of logical sense when actually neither client nor server will interpret it anyway as they will probably use the link relation name given for the URI.
GraphQL on the other hand is a basically just a query language which gives the client the power to request specific fields and elements it wants to retrieve from the server. It is, loosely speaking, some kind of SQL for the Web, or as Fielding termed it just a Remote Data Access (RDA). It therefore has to have some knowledge of the available data beforehand which couples clients somehow to the server. If the server will rename some of the fields, the client might not be able to retrieve that kind of information further, though I'm not a GraphQL expert.
As stated above, REST is often confused for a JSON based HTTP API that allows to perform queries on directly mapped DB entries/entities. Keep in mind that REST doesn't prohibit this, though its focus is on the decoupling of peers not the retrieval aspect of some Web exposed database entries. As Jim Webber pointed out in a great talk back in 2011 in REST you don't simply expose database tables, you create a domain application protocol which clients will follow along like in a text-based computer game or in a typical Webshop system on the internet.
Especially the linked introspection documentation of GraphQL reminds me of reflection in Java, which couples to the actual class model available. If something along the datamodel changes, how does the GraphQL interaction behave? Is it able to change and adapt? Is a client built for one API able to work with an other API out of the box? All these are basically requirements for a true RESTful client. It basically has to adept to changes in future as the server is free to evolve anytime. It further shouldn't assume certain endpoints returning certain types but use content type negotiation to request a representation it can work upon.
These should give you enough insights to determine for yourself whether GraphQL can be RESTful or not. In my opinion it isn't, but my insights into GraphQL are rather limited, TBH.
Because graphql publishes Metadata about its types, it's entirely plausible (I think) to build a graphql client that could consume any graphql endpoint ...
SOAP did the exact same thing, though it was still an RPC protocol. A client could look up the ...?wsdl information at run-time and then generate a request according to the schema defined in the WSDL dynamically, though what usually happened was that some pre-generated stub-classes were generated based on the WSDL data that got compiled into a specific client. A client dynamically generating a request still needed a routine that defines what message-type to create and what data the message required as input.
While SOAP could potentially define multiple endpoints within a WSDL, in most cases only one was defined though. This endpoint usually only operates on POST requests even when later on (SOAP 1.2) GET would have been possible also.
According to Fielding's thesis
REST uses a resource identifier to identify the particular resource involved in an interaction between components.
, what would be the resource identifier in GraphQL? GraphQL's documentation states that
... In contrast, GraphQL's conceptual model is an entity graph. As a result, entities in GraphQL are not identified by URLs. Instead, a GraphQL server operates on a single URL/endpoint, usually /graphql, and all GraphQL requests for a given service should be directed at this endpoint.
Similar to SOAP, all the request are targeted towards a single endpoint. This has some impact if you consider caching, which is a further constraint REST implies. How are responses cacheable if the URI is the key used to store the response in the cache?
While all of the aggregation stuff and the flexibility may be nice from a consumer perspective, they are, probably, not in line with the constraints of REST, though Fielding himself claimed that REST is not applicable in all situations and that designers should select a style that fits their needs as not every style is the "silver bullet" to each problem. Even Mike Amundsen stated that GraphQL violates at least 3 constraints imposed by the REST architecture, even though GraphQL seems to have changed the default retrieval method from POST to GET since.
Usually, if you aim for long-living APIs that should be free to evolve in future and that has to deal with lots of clients, especially ones not under your direct control, this is when REST starts to shine. Fielding admits that most developers have problems when thinking long-term. For a single frontend-to-backend system or for a tailor-made client interacting with the own API, REST is not the architecture one should probably follow.
Last but not least, in a later tweet Fielding stated
There is no such thing as a REST endpoint. There are resources. A countably infinite set of resources bound only by restrictions on URL length. A client can POST to a REST service to create a resource that is a GraphQL query, and then GET that resource with all benefits of REST…
which I interpret as, don't focus to much on justifying whether GraphQL is REST or not, but think about how you can integrate its benefits into the overall design.
My understanding of SOAP vs REST:
REST = JSON, simple consistent interface, gives you CRUD access to 'entities' (Abstractions of things which are not necessarily single DB rows), simpler protocol, no formally enforced 'contract' (e.g. the values an endpoint returns could change, though it shouldn't)
SOAP = XML, more complex interface, gives you access to 'services' (specific operations you can apply to entities, rather than allowing you to CRUD entities directly), formally enforced, pre-stated 'contract' (like a WSDL, where e.g. the return types are predefined and formalized)
Is that a broadly correct assessment?
What about a mixture?
If so, what do I call an API that is a mixture?
For example, If we have what at surface level looks like a REST API (returns JSON, no WSDL or formalized contract defined - but instead of giving you access to the 'entities' that the system manages (User, product, comment, etc) it instead gives you specific access to services and complex operations (/sendUserAnUpdate/1111, /makeCommentTextPurple/3333, /getAllCommentsByUserThisYear/2222) without having full coverage?
The 'services' already exist internally, and the team simply publishes access to them on a request by request basis, through what would otherwise look like a REST API.
Question:
What is the 'mixture' typically referred to as (besides, maybe, a bad API). Is there a word for it? or a concept I can refer to that'll make most developers understand what I'm referring to, without having to say the entire paragraph I did above?
Is it just "JSON SOAP API?", "A Service-based REST API?" - what would you call it?
Thanks!
Thanks!
If you take a look at all those so-called REST-APIs your observation might seem true, though REST actually is something completely different. It describes an architecture or a philosophy whose intent it is to decouple clients from servers, allowing the latter one to evolve in future without breaking clients. It is quite similar to the typical Web page interaction in that a server will teach a client on what it needs and only reacts on client-triggered requests. One has to be pretty careful and pendant when designing REST services as it is too easy to include a coupling that may affect clients when a change is introduced, especially with all the pragmatism around in (commercial) software engineering. Stefan Tilkov gave a great talk on REST back in 2014 that, alongside with Jim Webber or Asbjørn Ulsberg, can be used as introduction lectures to what REST is at its core.
The general premise in REST should always be that a server teaches clients what they need and what a server expects and offers choices to the client via links. If the server expects to receive data from the client it will send a form-esque representation to inform the client about the respective fields it supports and based on the affordance of the respective elements contained in the form a client knows whether to select one or multiple options, enter some free text or enter a date value and such. Unfortunately, most of the media-type formats that attempt to mimic HTML's forms are still in draft versions.
If you take a look at HTML forms in particular you might sense what I'm refering to. Each of the elements that may occur inside a form are well defined to avoid abmiguity and improve interoperability. This is defacto the ultimate goal in REST, having one client that is able to interact with a sheer amount of other services without having to be adapted to each single API explicitely.
The beauty of REST is, it isn't limited to a single representation form, i.e. JSON, in fact there is almost an infinite number of possible representation formats that could be exchanged in a REST environment. Plain application/json is a terrible media-type for REST applications IMO as it doesn't include any defintions in regards to links and forms and doesn't describe the semantics of certain fields that may be shipped in requests and responses. The lack of semantical description usually leads to typed resources where a recipient expects that receiving data from i.e. /api/users returns some specific user data, that may differ from host to host. If you skim through IANA's media type registry you will find a couple of media-type formats you could have used to transfer user-related data and any client supporting these representation formats whold be able to interact with this enpoint without any issues. Fielding himself claimed that
A REST API should spend almost all of its descriptive effort in defining the media type(s) used for representing resources and driving application state, or in defining extended relation names and/or hypertext-enabled mark-up for existing standard media types. Any effort spent describing what methods to use on what URIs of interest should be entirely defined within the scope of the processing rules for a media type (and, in most cases, already defined by existing media types). (Source)
Through content-type negotiation client and server will negotiate about a representation format both support and understand. The question therefore shouldn't be which one to support but how many you want to support. The more media-type your API or client is able to exchange payloads for, the more likely it will be to interact with other participants.
Most of those so-called REST APIs are in reality just RPC services exposed via HTTP that may or may not respect and support certain HTTP operations. HTTP thereby is just a transport layer whose domain is the transfer of files or data over the Web. Plenty of people still believe that you shouldn't put verbs in URIs when in reality a script or process usually doesn't (and shouldn't) care whether a URI contains a verb or not. The URI itself is just a pointer a client will follow and invoke when it is interested in receiving the payload. We humans are also not that much interested in the URI itself in regards to the content it may return after invoking that URI. The same holds true for arbitrary clients. It is more important what you ship along with that URI. On the Web a link can be annotated with certain text and/or link relation names that set the links content in relation to the current page. It may hint a client that certain content may be invoked before the whole response was parsed as it is quite likely that the client will also want to know about that. preload i.e. is such a link-relation name that hints the client about that. If certain domain-specific terms exist one might use an extension scheme as defined by Web linking or reuse common knowlege or special microformats.
The whole interaction in a REST environment is similar to playing a text-based computer game or following a certain process flow (i.e. ordering and paying produts) defined by an application domain protocol, that can be designed as a state machine. The client is therefore guided through the whole process. It basically just follows the orders the server gave it, with some choices to break out of the process (i.e. cancel the order before paying).
SOAP on the otherhand is, as you've stated, an XML-based RPC protocol reusing a subset of HTTP to exchange requests and responses. The likelihood that when you change something within your WSDL plenty of clients have to be adapted and recompiled are quite high. SOAP even defines its own security mechanism instead of reusing TLS, which requires explicit support by the clients therefore. As you have a one-to-one communication model due to the state that may be kept in process, scaling SOAP services isn't that easy. In a REST environment this is just a matter of adding a load-balancer before the server and then mirroring the server n-times. The load-balancer can send the request to any of the servers due to the stateless constraint
What is the 'mixture' typically referred to as (besides, maybe, a bad API). Is there a word for it? or a concept I can refer to that'll make most developers understand what I'm referring to, without having to say the entire paragraph I did above?
Is it just "JSON SOAP API?", "A Service-based REST API?" - what would you call it?
The general term for an API that communicates on top of HTTP would be Web API or HTTP API IMO. This article also uses this term. It also lists XML-RPC and JSON-RPC besides SOAP. I do agree with Voice though that you'll receive 5 answers on asking 4 people about the right term to use. While it would be convenient to have a respective term available everyone would agree upon, the reality shows that people are not that interested in a clear separation. Just look here at SO on the questions taged with rest. There is nothing wrong with not being "RESTful", though one should avoid the term REST for truly RPC services. Though I think we are already in a situation where the term REST can't be rescued from misusage and marketing purposes.
For something that requires external documentation to use and that ships with its own custom, non-standardized representation format or that just exposes CRUD for domain objects I'd add -RPC to it, as this is more or less what it is at its heart. So if the API sends JSON and the representation to expect is documented via Swagger or some other external documentationJSON-RPC would probably the most fitting name IMO.
To sum up this post, I hope I could shed some light on what REST truly is and how your observation is flawed by all those pragmatic attempts that unfortunately are RPC through and through. If you change something within their implementation, how many clients will break? In addition to that you can't reuse the client that you've implemented for API A to interact with API B (of a different company or vendor) out of the box and therefore have to either adapt your client or create a new one solely for that API. This is true RPC and therfore should be reflected in the name somehow to hint developers about future expectations. Unfortunately, the process of naming things propperly, especially in regards to REST, seems already lost. There is a fine but tiny group who attempt to spread the true meaning, like Voice, Cassio and some others, though it is like fighting windmills. The best advice here would be to first discuss the naming conventions and what each participant understand on which term and then agree on a naming scheme everyone agrees on to avoid future confusion.
My understanding of SOAP vs REST
...
Is that a broadly correct assessment?
No.
REST is an "architectural style", which is to say a coordinated collection of architectural constraints. The World Wide Web is an example of an application built using the REST architectural style.
SOAP is a transport agnostic message protocol specification, based on XML Information Set
If so, what do I call an API that is a mixture?
I don't think you are going to find an authoritative terminology here. Colloquially, you are likely to hear the broad umbrella term "web api" to describe an HTTP API that isn't "RESTful".
The whole space is rather polluted by semantic diffusion.
I have a Soap service that is running over http. Is this also a REST service. What are the criteria that would make it a REST service. What are the criteria that would definitively exclude it as a REST service? There are posts (e.g. here) that compare REST and Soap but do not seem to answer this question directly. My answer is: Yes, a Soap service at its functional level is an http request that returns an XML payload where state is not maintained by the server and is therefore a REST service.
Fielding stated in his dissertation:
REST provides a set of architectural constraints that, when applied as a whole, emphasizes scalability of component interactions, generality of interfaces, independent deployment of components, and intermediary components to reduce interaction latency, enforce security, and encapsulate legacy systems.
If you compare the above mentioned properties with Web-browsing, you will find plenty of similarities between both as Fielding just took the concepts which made the Web such a success and applied it onto a more general field, that also should allow applications to "surf the Web".
In order to rightfully call an architecture REST it has to support self-descriptiveness, scalability and cacheability while also respecting and adhering to the rules and semantics outlined by the underlying transport protocol and enforce the usage of well-defined standards, such as media types, link relation names, HTTP operations, URI standards, ...
Self-descriptiveness of a service is utilized by HATEOAS (or hate-us, as I tend to pronounce it, as people like me who see the benefit in REST always have to stress this key-term, which therefore also ended up in its own meme). Via HATEOAS a client is served by the server with all the available "actions" a client could take from the current "state" the client is in. An "action" here is just a link with an accompanying link-relation name a client can use to deduce when to best invoke that URI. The media-type the response was returned for may define what to do with such links. HTML i.e. states that on clicking a link a GET request is triggered and the content of the link is loaded either in the current pane or in a new tab, depending on the arguments the link has. Other media-types may defines something similar or something different at all. The general motto here, though, is: proceeding thru exploring. The interaction model in a REST architecture is therefore best designed as affordance and state machine while the actual service should follow more like a Web site approach where a server is teaching a client, i.e. on how a request has to look like and where to send the request to (similar to HTML forms).
As plenty of Web pages are more or less static and a majority of requests are retrieval focused, the Web heavily relies on caching. The same is generally expected from REST APIs as well, hence the strong requirement for cacheability here, as this could reduce the workload on servers quite notably if proper caching is in place.
By keeping client state away from servers this also allows to add new copies of a service onto new servers located behind a load balancer or new regions and thus increase scalability. A client usually does not care where it retrieves the data from, hence a server might just return a URI pointing to a clone instead of itself.
SOAP on the other hand is RPC, like Java's remote method invocation (RMI) or CORBA, where you have an own interface definition language (IDL) to generate client side stub-code for you, that contains the actual logic on how to transform certain objects into byte streams and how to send them over the wire, where you invoke certain methods.
Where SOAP violates REST constraints is clearly by the lack of caching support as well as out-of-band knowledge that needs to be available before actually using a client. SOAP messages are usually always exchanged as POST operations, which are not cacheable by default. Certain HTTP headers are available to allow intermediary servers to cache the response though SOAP doesn't make use of such and thus lacks general support for it.
A client developed for SOAP endpoint A will most likely also not be interoperable with a further SOAP endpoint B ran by a different company. While one might argue that a Web client also does not know how to process each of the different media-types, browsers usually provide plugin mechanism to load that kind of knowledge into the client. A media type is in addition to that also standardized, at least it should be, and may therefore be usable with plenty of servers (think of Flash-support i.e.). A further problem SOAP services have is, that once anything is changed in the WSDL definition clients not aware of the update will most likely stop to work with that updated service until the client code is updated to work with the latest version of the generated stub classes.
In regards to the XML format exchanged in SOAP: While technically it is doable for a REST service to return a SOAP XML payload, the format itself lacks support of HATEOAS, which is a necessity and not an option. How should a client make further choices based on the received response simply on the content received without any a-priori knowledge of the API itself?
I hope you can see that SOAP lacks support of caching, may have problems with scalability as well as leads to a tight coupling of clients to the actual API. The lack of HATEOAS support by the SOAP message envelop/header/body also does not allow clients to explore the API freely and thus adapt to server changes automatically.
Proper REST services follow the architectural guidelines spelled out in chapter five of Roy Fielding's dissertation. Most people erroneously use the term "REST API" when they really mean "HTTP API". Statelessness is a necessary but not sufficient condition for an API to adhere to the REST architectural guidelines.
Can anyone explain difference between Swagger & HATEOAS. I can Search many time but no buddy can explain the proper detailed answer this two aspects.
The main difference between Swagger and HATEOAS IMO, which is not covered in the accepted answer, is, that Swagger is only needed for RPC'esque APIs. Such APIs, however, have actually hardly anything to do with REST.
There is a further, widespread misconception that anything exchanged via HTTP is automatically RESTful (~ in accordance with the REST archtitectural style), which it is not. REST just defines a set of constraints that are not choices or options but are mandatory. From start to finish. There is nothing wrong from being not RESTful, but it is wrong to term such an architecture REST.
Swagger describe the operations that can be performed on an endpoint and the payload (including headers and the expected representation formats) that needs to be sent to the service and also describe what a client might expect as response. This allows Swagger to be used both as documentation as well as testing-framework for the API. Due to the tight coupling of Swagger to the API it behaves much like a typical RPC service description, i.e. similar to WSDL files in SOAP or stub or skeletton classes in RMI or CORBA. If either the endpoint changes or something in the payload changes, clients implementing against a Swagger documentation will probably break over time just reintroducing the same problems typical RPC implementations have.
REST and HATEOAS, on the other side, are designed for disovery and further development. REST isn't a protocol but an architectural style to start with that describes the interaction flow between a client and server in a distributed system. It basically took the concepts which made the Web so successful and translated it onto the application layer. So the same concepts that apply to the browsable Web also apply to REST. Therefore it is no miracle that also HATEOAS (the usage of and support for links, link relations and link names) behave similar to the Web.
On designing a REST architecture it is benefitial to think of a state machine where a server provides all of the information a client needs to take further actions. Asbjørn Ulsberg held a great talk back in 2016 where he explains affordances and how a state machine might be implemented through HATEOAS. Besides common or standardized media-types and relation names no out-of-band knowledge is necessary to interact with the service further. In the case of the toaster example Asbjørn gave in his talk, a toaster may have the states off, on, heating and idle where turning a toaster on will lead to a state transition from off to on followed by a transition to heating till a certain temperature is reached where the state is transitioned to idle and switches between idle and heating till the toaster is turned off.
HATOAS will provide a client with the information on the current state and include links a client can invoke to transition to the next state, i.e. turning the toaster off again. It's important to stress here, that a client is provided by the server with every action the client might perform next. There is no need for a client implementor to consult any proprietary API documentation in order for a client to be able to interact with a REST service. Further, URIs do not have to be meaningful or designed to convey a semantical-expressive structure as clients will determine whether invoking that URI makes sense via the link-relation name. Such relation names are either specified by IANA, by a common approach such as Dublin Core or schema.org or by absolut URIs acting as extension attributes which might point to a human-readable description, which further might be propagated to the user via mouse-over tooltips or such.
I hope you can see by yourself that Swagger is only needed to describe RPC Web-APIs rather than applications that follow the REST architectural design. Messages exchanged via REST APIs should include all the information needed by a client to make informed choices on the next state transition. As such it is benefitial to design such message flows and interactions as state machine.
Update:
How are Swagger and HATEOAS mutually exclusive? The former documents your endpoints (making auto-generating code possible) and the latter adds meta-information to your endpoints which tell the consumer what they can do (i.e. which other endpoints are available). These are very different things.
I never stated that they are mutually exclusive, just that they serve two different purposes, where if you follow one approach the other gets more or less useless. Using both does not make any sense though.
Let's move the discussion to the Web domain as this is probably more easily understandable and REST is de facto just a generalization of the concepts used on the Web, so doing this step is just natural and also a good recommendation in terms of designing REST architectures in general. Think of a case where you as a user want to send some data to the server. You have never used the service before so you basically don't know how a request has to look like.
In Swagger you would call the endpoint documentation, select the option that most likely might solve your task, read up on how the request needs to look like and hack a test-case into your application that ends up generating a HTTP request that is sent to the respective location. Auto-generating code might spare you some hacking time, though you still need to integrate the stub classes into your application and test the whole thing at least once just to be safe. If you later on need to integrate a second service of that API or of yet an other API in general, you need to start from the beginning and look up the Swagger documentation, generate or hack the interaction code and integrate it into your domain. Plenty of manual steps involved and in cases of API changes you need to update your client as otherwise it might stop working.
In the Web example however, you just start your browser/Web client, invoke the respective URI that allows you to send the data to the server and the server will most likely send you a HTML form you just need to fill out and click the send button which automatically sends the request to the server which will start to process it. This is HATEOAS. You used the given controls to drive your workflow. The server taught your client every little detail it needed to make a valid request. It served your client with the target URI to send the request to, the HTTP method it should use and most often also implicitly the media type the payload should be in. In addition to that it also gave your clients a skeleton of the expected and/or supported elements the payload should contain. I.e. the form may require you to fill out a couple of input fields, select among a given set of choices or use some other controls such as a date or time picker value that is translated to a valid date or time representation for you. All you needed to do was to invoke the respective resource in your Web client. No auto-generation, no integration into your browser/application. Using other services (from the same or different providers) will, most likely, just work the same way so no need to change or update your HTTP client (browser) as long as the media-type request and responses are exchanged are supported.
In the case where you rely on Swagger RPC'esque documentation, that documentation is the truth on how to interact with the service. Mixing in some HATEOAS information doesn't provide you any benefits. In the Swagger case, carrying around additional meta-information that bloat up the request/response for no obvious reasons, as all the required information is given in the reference documentation, will, with some certainty, lead to people starting questioning the sanity of the developers of that service and ask for payload reduction. Just look here at SO for a while and you will find enough question asking on how to optimize the interaction further and further and reducing message size to a minimum as they process every little request and don't make use of response caching at all. In the HATEOAS case, pointing to an external reference is just useless as peers in such an architecture most likely already have support for the required necessities, such as URI, HTTP and the respective media types, implemented into it. In cases where custom media-types are used, support can be added at runtime via plug-ins or add-ons dynamically (if supported).
So, Swagger and HATEOAS are not mutually exclusive but the other gets more or less useless once you decided for one route or the other.
Swagger: Swagger aids in development across the entire API lifecycle, from design and documentation, to test and deployment. (Refer to swagger.io)
HATEOAS: Hypermedia as the Engine of Application State
An Ion Form is a Collection Object where the value member array contains Form Fields. Ion Forms ensure that resource transitions (links) that support data submissions can be discovered automatically (colloquially referred to as HATEOAS). (Refer to https://ionspec.org/)
One is a framework for supporting designing and testing for APIs, the other is an API design architecture.
Building a RESTful API is not a binary concept. That is why we use the Richardson maturity model in order to measure how RESTful an API is.
Based on this maturity model
At level 0 we provide mechanisms for client of the API to call some methods on the server (Simple RPC)
At level 1 we expose resources on the server so the client of the API can have direct access to the resources that it requires (exposing Resources)
At level 2 we provide a uniform way for the client of the api to interact with the API (exposed resources) and the HTTP protocol has these methods (using HTTP verbs to interact with resources).
the ultimate step is to make our api explorable by the client. HATEOAS provides such functionality (over HTTP) meaning that it adds relevant links and affordances (extra methods) that can executed on the resource so the client of the API can understand its behavior.
Based on these definitions in properly designed RESTful API there is no coupling between client and server and client can interact with the exposed endpoints an discover them.
On the other hand, swagger is a tool that helps you document your API along with some extra goodies (code generators).
I believe that Swagger (with the help of swagger Hub) provides services for implementing a RESTful endpoint with maturity levels up to 2. But it does not go any further and it does not provide proper support of HATEOAS.
You can define your resources and HTTP verbs in (json/yml) files. And based on this definition Swagger can generate API documentation and the extra goodies (client stubs and skeletal implementation of the server API).
For all those people who have worked with Java RMI, SOAP,... the extra goodies part is a reminder of old technologies where there was tight coupling between Client and Server because the stubs and skeletal implementations are all built based on the same API definition file.
I have read articles about the differences between SOAP and REST as a web service communication protocol, but I think that the biggest advantages for REST over SOAP are:
REST is more dynamic, no need to create and update UDDI(Universal Description, Discovery, and Integration).
REST is not restricted to only XML format. RESTful web services can send plain text/JSON/XML.
But SOAP is more standardized (E.g.: security).
So, am I correct in these points?
Unfortunately, there are a lot of misinformation and misconceptions around REST. Not only your question and the answer by #cmd reflect those, but most of the questions and answers related to the subject on Stack Overflow.
SOAP and REST can't be compared directly, since the first is a protocol (or at least tries to be) and the second is an architectural style. This is probably one of the sources of confusion around it, since people tend to call REST any HTTP API that isn't SOAP.
Pushing things a little and trying to establish a comparison, the main difference between SOAP and REST is the degree of coupling between client and server implementations. A SOAP client works like a custom desktop application, tightly coupled to the server. There's a rigid contract between client and server, and everything is expected to break if either side changes anything. You need constant updates following any change, but it's easier to ascertain if the contract is being followed.
A REST client is more like a browser. It's a generic client that knows how to use a protocol and standardized methods, and an application has to fit inside that. You don't violate the protocol standards by creating extra methods, you leverage on the standard methods and create the actions with them on your media type. If done right, there's less coupling, and changes can be dealt with more gracefully. A client is supposed to enter a REST service with zero knowledge of the API, except for the entry point and the media type. In SOAP, the client needs previous knowledge on everything it will be using, or it won't even begin the interaction. Additionally, a REST client can be extended by code-on-demand supplied by the server itself, the classical example being JavaScript code used to drive the interaction with another service on the client-side.
I think these are the crucial points to understand what REST is about, and how it differs from SOAP:
REST is protocol independent. It's not coupled to HTTP. Pretty much like you can follow an ftp link on a website, a REST application can use any protocol for which there is a standardized URI scheme.
REST is not a mapping of CRUD to HTTP methods. Read this answer for a detailed explanation on that.
REST is as standardized as the parts you're using. Security and authentication in HTTP are standardized, so that's what you use when doing REST over HTTP.
REST is not REST without hypermedia and HATEOAS. This means that a client only knows the entry point URI and the resources are supposed to return links the client should follow. Those fancy documentation generators that give URI patterns for everything you can do in a REST API miss the point completely. They are not only documenting something that's supposed to be following the standard, but when you do that, you're coupling the client to one particular moment in the evolution of the API, and any changes on the API have to be documented and applied, or it will break.
REST is the architectural style of the web itself. When you enter Stack Overflow, you know what a User, a Question and an Answer are, you know the media types, and the website provides you with the links to them. A REST API has to do the same. If we designed the web the way people think REST should be done, instead of having a home page with links to Questions and Answers, we'd have a static documentation explaining that in order to view a question, you have to take the URI stackoverflow.com/questions/<id>, replace id with the Question.id and paste that on your browser. That's nonsense, but that's what many people think REST is.
This last point can't be emphasized enough. If your clients are building URIs from templates in documentation and not getting links in the resource representations, that's not REST. Roy Fielding, the author of REST, made it clear on this blog post: REST APIs must be hypertext-driven.
With the above in mind, you'll realize that while REST might not be restricted to XML, to do it correctly with any other format you'll have to design and standardize some format for your links. Hyperlinks are standard in XML, but not in JSON. There are draft standards for JSON, like HAL.
Finally, REST isn't for everyone, and a proof of that is how most people solve their problems very well with the HTTP APIs they mistakenly called REST and never venture beyond that. REST is hard to do sometimes, especially in the beginning, but it pays over time with easier evolution on the server side, and client's resilience to changes. If you need something done quickly and easily, don't bother about getting REST right. It's probably not what you're looking for. If you need something that will have to stay online for years or even decades, then REST is for you.
REST vs SOAP is not the right question to ask.
REST, unlike SOAP is not a protocol.
REST is an architectural style and a design for network-based software architectures.
REST concepts are referred to as resources. A representation of a resource must be stateless. It is represented via some media type. Some examples of media types include XML, JSON, and RDF. Resources are manipulated by components. Components request and manipulate resources via a standard uniform interface. In the case of HTTP, this interface consists of standard HTTP ops e.g. GET, PUT, POST, DELETE.
#Abdulaziz's question does illuminate the fact that REST and HTTP are often used in tandem. This is primarily due to the simplicity of HTTP and its very natural mapping to RESTful principles.
Fundamental REST Principles
Client-Server Communication
Client-server architectures have a very distinct separation of concerns. All applications built in the RESTful style must also be client-server in principle.
Stateless
Each client request to the server requires that its state be fully represented. The server must be able to completely understand the client request without using any server context or server session state. It follows that all state must be kept on the client.
Cacheable
Cache constraints may be used, thus enabling response data to be marked as cacheable or not-cacheable. Any data marked as cacheable may be reused as the response to the same subsequent request.
Uniform Interface
All components must interact through a single uniform interface. Because all component interaction occurs via this interface, interaction with different services is very simple. The interface is the same! This also means that implementation changes can be made in isolation. Such changes, will not affect fundamental component interaction because the uniform interface is always unchanged. One disadvantage is that you are stuck with the interface. If an optimization could be provided to a specific service by changing the interface, you are out of luck as REST prohibits this. On the bright side, however, REST is optimized for the web, hence incredible popularity of REST over HTTP!
The above concepts represent defining characteristics of REST and differentiate the REST architecture from other architectures like web services. It is useful to note that a REST service is a web service, but a web service is not necessarily a REST service.
See this blog post on REST Design Principles for more details on REST and the above stated bullets.
EDIT: update content based on comments
SOAP (Simple Object Access Protocol) and REST (Representation State Transfer) both are beautiful in their way. So I am not comparing them. Instead, I am trying to depict the picture, when I preferred to use REST and when SOAP.
What is payload?
When data is sent over the Internet, each unit transmitted includes both header information and the actual data being sent. The header identifies the source and destination of the packet, while the actual data is referred to as the payload. In general, the payload is the data that is carried on behalf of an application and the data received by the destination system.
Now, for example, I have to send a Telegram and we all know that the cost of the telegram will depend on some words.
So tell me among below mentioned these two messages, which one is cheaper to send?
<name>Arin</name>
or
"name": "Arin"
I know your answer will be the second one although both representing the same message second one is cheaper regarding cost.
So I am trying to say that, sending data over the network in JSON format is cheaper than sending it in XML format regarding payload.
Here is the first benefit or advantages of REST over SOAP. SOAP only support XML, but REST supports different format like text, JSON, XML, etc. And we already know, if we use Json then definitely we will be in better place regarding payload.
Now, SOAP supports the only XML, but it also has its advantages.
Really! How?
SOAP relies on XML in three ways
Envelope – that defines what is in the message and how to process it.
A set of encoding rules for data types, and finally the layout of the procedure calls and responses gathered.
This envelope is sent via a transport (HTTP/HTTPS), and an RPC (Remote Procedure Call) is executed, and the envelope is returned with information in an XML formatted document.
The important point is that one of the advantages of SOAP is the use of the “generic” transport but REST uses HTTP/HTTPS. SOAP can use almost any transport to send the request but REST cannot. So here we got an advantage of using SOAP.
As I already mentioned in above paragraph “REST uses HTTP/HTTPS”, so go a bit deeper on these words.
When we are talking about REST over HTTP, all security measures applied HTTP are inherited, and this is known as transport level security and it secures messages only while it is inside the wire but once you delivered it on the other side you don’t know how many stages it will have to go through before reaching the real point where the data will be processed. And of course, all those stages could use something different than HTTP.So Rest is not safer completely, right?
But SOAP supports SSL just like REST additionally it also supports WS-Security which adds some enterprise security features. WS-Security offers protection from the creation of the message to it’s consumption. So for transport level security whatever loophole we found that can be prevented using WS-Security.
Apart from that, as REST is limited by it's HTTP protocol so it’s transaction support is neither ACID compliant nor can provide two-phase commit across distributed transnational resources.
But SOAP has comprehensive support for both ACID based transaction management for short-lived transactions and compensation based transaction management for long-running transactions. It also supports two-phase commit across distributed resources.
I am not drawing any conclusion, but I will prefer SOAP-based web service while security, transaction, etc. are the main concerns.
Here is the "The Java EE 6 Tutorial" where they have said A RESTful design may be appropriate when the following conditions are met. Have a look.
Hope you enjoyed reading my answer.
REST(REpresentational State Transfer)
REpresentational State of an Object is Transferred is REST i.e. we don't send Object, we send state of Object.
REST is an architectural style. It doesn’t define so many standards like SOAP. REST is for exposing Public APIs(i.e. Facebook API, Google Maps API) over the internet to handle CRUD operations on data. REST is focused on accessing named resources through a single consistent interface.
SOAP(Simple Object Access Protocol)
SOAP brings its own protocol and focuses on exposing pieces of application logic (not data) as services. SOAP exposes operations. SOAP is focused on accessing named operations, each operation implement some business logic. Though SOAP is commonly referred to as web services this is misnomer. SOAP has a very little if anything to do with the Web. REST provides true Web services based on URIs and HTTP.
Why REST?
Since REST uses standard HTTP it is much simpler in just about ever way.
REST is easier to implement, requires less bandwidth and resources.
REST permits many different data formats where as SOAP only permits XML.
REST allows better support for browser clients due to its support for JSON.
REST has better performance and scalability. REST reads can be cached, SOAP based reads cannot be cached.
If security is not a major concern and we have limited resources. Or we want to create an API that will be easily used by other developers publicly then we should go with REST.
If we need Stateless CRUD operations then go with REST.
REST is commonly used in social media, web chat, mobile services and Public APIs like Google Maps.
RESTful service return various MediaTypes for the same resource, depending on the request header parameter "Accept" as application/xml or application/json for POST and /user/1234.json or GET /user/1234.xml for GET.
REST services are meant to be called by the client-side application and not the end user directly.
ST in REST comes from State Transfer. You transfer the state around instead of having the server store it, this makes REST services scalable.
Why SOAP?
SOAP is not very easy to implement and requires more bandwidth and resources.
SOAP message request is processed slower as compared to REST and it does not use web caching mechanism.
WS-Security: While SOAP supports SSL (just like REST) it also supports WS-Security which adds some enterprise security features.
WS-AtomicTransaction: Need ACID Transactions over a service, you’re going to need SOAP.
WS-ReliableMessaging: If your application needs Asynchronous processing and a guaranteed level of reliability and security. Rest doesn’t have a standard messaging system and expects clients to deal with communication failures by retrying.
If the security is a major concern and the resources are not limited then we should use SOAP web services. Like if we are creating a web service for payment gateways, financial and telecommunication related work then we should go with SOAP as here high security is needed.
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IMHO you can't compare SOAP and REST where those are two different things.
SOAP is a protocol and REST is a software architectural pattern. There is a lot of misconception in the internet for SOAP vs REST.
SOAP defines XML based message format that web service-enabled applications use to communicate each other over the internet. In order to do that the applications need prior knowledge of the message contract, datatypes, etc..
REST represents the state(as resources) of a server from an URL.It is stateless and clients should not have prior knowledge to interact with server beyond the understanding of hypermedia.
First of all: officially, the correct question would be web services + WSDL + SOAP vs REST.
Because, although the web service, is used in the loose sense, when using the HTTP protocol to transfer data instead of web pages, officially it is a very specific form of that idea. According to the definition, REST is not "web service".
In practice however, everyone ignores that, so let's ignore it too
There are already technical answers, so I'll try to provide some intuition.
Let's say you want to call a function in a remote computer, implemented in some other programming language (this is often called remote procedure call/RPC). Assume that function can be found at a specific URL, provided by the person who wrote it. You have to (somehow) send it a message, and get some response. So, there are two main questions to consider.
what is the format of the message you should send
how should the message be carried back and forth
For the first question, the official definition is WSDL. This is an XML file which describes, in detailed and strict format, what are the parameters, what are their types, names, default values, the name of the function to be called, etc. An example WSDL here shows that the file is human-readable (but not easily).
For the second question, there are various answers. However, the only one used in practice is SOAP. Its main idea is: wrap the previous XML (the actual message) into yet another XML (containing encoding info and other helpful stuff), and send it over HTTP. The POST method of the HTTP is used to send the message, since there is always a body.
The main idea of this whole approach is that you map a URL to a function, that is, to an action. So, if you have a list of customers in some server, and you want to view/update/delete one, you must have 3 URLS:
myapp/read-customer and in the body of the message, pass the id of the customer to be read.
myapp/update-customer and in the body, pass the id of the customer, as well as the new data
myapp/delete-customer and the id in the body
The REST approach sees things differently. A URL should not represent an action, but a thing (called resource in the REST lingo). Since the HTTP protocol (which we are already using) supports verbs, use those verbs to specify what actions to perform on the thing.
So, with the REST approach, customer number 12 would be found on URL myapp/customers/12. To view the customer data, you hit the URL with a GET request. To delete it, the same URL, with a DELETE verb. To update it, again, the same URL with a POST verb, and the new content in the request body.
For more details about the requirements that a service has to fulfil to be considered truly RESTful, see the Richardson maturity model. The article gives examples, and, more importantly, explains why a (so-called) SOAP service, is a level-0 REST service (although, level-0 means low compliance to this model, it's not offensive, and it is still useful in many cases).
Among many others already covered in the many answers, I would highlight that SOAP enables to define a contract, the WSDL, which define the operations supported, complex types, etc.
SOAP is oriented to operations, but REST is oriented at resources.
Personally I would select SOAP for complex interfaces between internal enterprise applications, and REST for public, simpler, stateless interfaces with the outside world.
Addition for:
++ A mistake that’s often made when approaching REST is to think of it as “web services with URLs”—to think of REST as another remote procedure call (RPC) mechanism, like SOAP, but invoked through plain HTTP URLs and without SOAP’s hefty XML namespaces.
++ On the contrary, REST has little to do with RPC. Whereas RPC is service oriented and focused on actions and verbs, REST is resource oriented, emphasizing the things and nouns that comprise an application.
A lot of these answers entirely forgot to mention hypermedia controls (HATEOAS) which is completely fundamental to REST. A few others touched on it, but didn't really explain it so well.
This article should explain the difference between the concepts, without getting into the weeds on specific SOAP features.
REST API
RESTful APIs are the most famous type of API. REST stands REpresentational State Transfer.
REST APIs are APIs that follow standardized principles, properties, and constraints.
You can access resources in the REST API using HTTP verbs.
REST APIs operate on a simple request/response system. You can send a request using these HTTP methods:
GET
POST
PUT
PATCH
DELETE
TRACE
OPTIONS
CONNECT
HEAD
Here are the most common HTTP verbs
GET (read existing data)
POST (create a new response or data)
PATCH (update the data)
DELETE (delete the data)
The client can make requests using HTTP verbs followed by the endpoint.
The endpoint (or route) is the URL you request for. The path determines the resource you’re requesting.
When you send a request to an endpoint, it responds with the relevant data, generally formatted as JSON, XML, plain text, images, HTML, and more.
REST APIs can also be designed with many different endpoints that return different types of data. Accessing multiple endpoints with a REST API requires various API calls.
An actual RESTful API follows the following five constraints:
Client-Server Architecture
The client requests the data from the server with no third-party interpretation.
Statelessness
Statelessness means that every HTTP request happens in complete isolation. Each request contains the information necessary to service the request. The server never relies on information from previous requests. There’s no state.
Cacheability
Responses can be explicitly or implicitly defined as cacheable or non-cacheable to improve scalability and performance. For example, enabling the cache of GET requests can improve the response times of requests for resource data.
Layering
Different layers of the API architecture should work together, creating a scalable system that is easy to update or adjust.
Uniform Interface
Communication between the client and the server must be done in a standardized language that is independent of both. This improves scalability and flexibility.
REST APIs are a good fit for projects that need to be
Flexible
Scalable
Fast
SOAP API
SOAP is a necessary protocol that helped introduce the widespread use of APIs.
SOAP is the acronym for Simple Object Access Protocol.
SOAP is a standardized protocol that relies on XML to make requests and receive responses.
Even though SOAP is based on XML, the SOAP protocol is still in wide usage.
SOAP APIs make data available as a service and are typically used when performing transactions involving multiple API calls or applications where security is the primary consideration.
SOAP was initially developed for Microsoft in 1998 to provide a standard mechanism for integrating services on the internet regardless of the operating system, object model, or programming language.
The “S” in SOAP stands for Simple, and for a good reason — SOAP can be used with less complexity as it requires less coding in the app layer for transactions, security, and other functions.
SOAP has three primary characteristics:
Extensibility of SOAP API
SOAP allows for extensions that introduce more robust features, such as Windows Server Security, Addressing, and more.
Neutrality of SOAP API
SOAP is capable of operating over a wide range of protocols, like UDP, JMS, SMTP, TCP, and HTTP.can operate.
Independence of SOAP API
SOAP API responses are purely based on XML. Therefore SOAP APIs are platform and language independent.
Developers continue to debate the pros and cons of using SOAP and REST. The best one for your project will be the one that aligns with your needs.
SOAP APIs remain a top choice for corporate entities and government organizations that prioritize security, even though REST has largely dominated web applications.
SOAP is more secure than REST as it uses WS-Security for transmission along with Secure Socket Layer
SOAP also has more excellent transactional reliability, which is another reason why SOAP historically has been favored by the banking industry and other large entities.
What is REST
REST stands for representational state transfer, it's actually an architectural style for creating Web API which treats everything(data or functionality) as recourse.
It expects; exposing resources through URI and responding in multiple formats and representational transfer of state of the resources in stateless manner. Here I am talking about two things:
Stateless manner: Provided by HTTP.
Representational transfer of state: For example if we are adding an employee. .
into our system, it's in POST state of HTTP, after this it would be in GET state of HTTP, PUT and DELETE likewise.
REST can use SOAP web services because it is a concept and can use any protocol like HTTP, SOAP.SOAP uses services interfaces to expose the business logic. REST uses URI to expose business logic.
REST is not REST without HATEOAS. This means that a client only knows the entry point URI and the resources are supposed to return links the client should follow. Those fancy documentation generators that give URI patterns for everything you can do in a REST API miss the point completely. They are not only documenting something that's supposed to be following the standard, but when you do that, you're coupling the client to one particular moment in the evolution of the API, and any changes on the API have to be documented and applied, or it will break.
HATEOAS, an abbreviation for Hypermedia As The Engine Of Application State, is a constraint of the REST application architecture that distinguishes it from most other network application architectures. The principle is that a client interacts with a network application entirely through hypermedia provided dynamically by application servers. A REST client needs no prior knowledge about how to interact with any particular application or server beyond a generic understanding of hypermedia. By contrast, in some service-oriented architectures (SOA), clients and servers interact through a fixed interface shared through documentation or an interface description language (IDL).
Reference 1
Reference 2
Although SOAP and REST share similarities over the HTTP protocol, SOAP is a more rigid set of messaging patterns than REST. The rules in SOAP are relevant because we can’t achieve any degree of standardization without them. REST needs no processing as an architecture style and is inherently more versatile. In the spirit of information exchange, both SOAP and REST depend on well-established laws that everybody has decided to abide by.
The choice of SOAP vs. REST is dependent on the programming language you are using the environment you are using and the specifications.
To answer this question it’s useful to understand the evolution of the architecture of distributed applications from simple layered architectures, to object & service based, to resources based, & nowadays we even have event based architectures. Most large systems use a combination of styles.
The first distributed applications had layered architectures. I'll assume everyone here knows what layers are. These structures are neatly organized, and can be stacks or cyclical structures. Effort is made to maintain a unidirectional data flow.
Object-based architectures evolved out of layered architectures and follow a much looser model. Here, each component is an object (often called a distributed object). The objects interact with one another using a mechanism similar to remote procedure calls - when a client binds to a distributed object it loads an implementation of the objects interface into its address space. The RPC stub can marshal a request & receive a response. Likewise the objects interface on the server is an RPC style stub. The structure of these object based systems is not as neatly organized, it looks more like an object graph.
The interface of a distributed object conceals its implementation. As with layered components, if the interface is clearly defined the internal implementation can be altered - even replaced entirely.
Object-based architectures provide the basis for encapsulating services. A service is provided by a self-contained entity, though internally it can make use of other services. Gradually object-based architectures evolved into service-oriented architectures (SOAs).
With SOA, a distributed application is composed of services. These services can be provided across administrative domains - they may be available across the web (i.e. a storage service offered by a cloud provider).
As web services became popular, and more applications started using them, service composition (combining services to form new ones) became more important. One of the problems with SOA was that integrating different services could become extremely complicated.
While SOAP is a protocol, its use implies a service oriented architecture. SOAP attempted to provide a standard for services whereby they would be composable and easily integrated.
Resource-based architectures were a different approach to solving the integration problems of SOA. The idea is to treat the distributed system as a giant collection of resources that are individually managed by components.
This led to the development of RESTful architectures. One thing that characterizes RESTful services is stateless execution. This is different than SOA where the server maintains the state.
So… how do service-specific interfaces, as provided by service-oriented architectures (including those that use SOAP) compare with resource-based architecture like REST?
While REST is simple, it does not provide a simple interface for complex communication schemes. For example, if you are required to use transactions REST is not appropriate, it is better to keep the complex state encapsulated on the server than have the client manage the transaction. But there are many scenarios where the orthogonal use of resources in RESTful architectures greatly simplifies integration of services in what would otherwise mean an explosion of service interfaces. Another tradeoff is resource-based architectures put more complexity on the client & increase traffic over the network while service-based increase the complexity of the server & tax its memory & CPU resources.
Some people have also mentioned common HTTP services or other services that do not satisfy the requirements of RESTful architecture or SOAP. These too can be categorized as either service-based or resource-based. These have the advantage of being simpler to implement. You'd only use such an approach if you knew your service will never need to be integrated across administrative domains since this makes no attempt at fixing the integration issues that arise.
These sorts of HTTP-based services, especially Pseudo-RESTful services are still the most common types. Implementing SOAP is complicated and should only be used if you really need it - i.e. you need a service that's easily integrated across domains and you want it to have a service-interface. There are still cases where this is needed. A true RESTful service is also difficult to implement, though not as difficult as SOAP.