Can anybody explain the usage of EAnnotation in ecore, in terms of its specific fields (i.e.,
Source,
Details,
EModel Element,
Contents, and
References). I looked at its API documentation here, but could not get that much from there.
I am looking for a kind of guideline to explain by example what are the purpose of having annotations with such fields in ecore.
I asked this question in Eclipse EMF forum and here is an answer.
There is also an answer to this question here..
However, I briefly provide an answer to this question:
Generally EAnnotations are used in Ecore to encode any kind of information which is not captured by Ecore at first place. For example, they are used in OCLInECore to hold OCL constraints, or in genmodel to store code generation related information and etc.
Source is used to identify the type of annotation. It is usually populated with a URI, to uniquely identify the type of annotation.
Details is a set of (key,value) pairs to hold detailed information regarding this annotation. Actually this is the place annotation data are really stored.
The rest is (quoted from here):
EModel Element ,
"An EAnnotation is itself an EModelElement, so can also be annotated. It's not
often used, but would allow you to build a complex structure.."
Contents
EAnnotations can contain arbitrary other objects. This is also not
often used, and if you do use it, you can't generate a normal
XyzPackageImpl but must ensure that the GenPackage specifies "Initialize
by Loading"..."
References.
"EAnnotations can refer to arbitrary other objects. This is also not
often used, and the same caveat applies and for the contents..."
Related
I am reading up on Schema.org to be able to add the markup to a website I am working on. However, I'm already running into something I don't understand.
In the example for Product, it shows you should have a div whose itemprop is of type offers, but in the Product definition at http://schema.org/Product, I don't see offers as a property of Product at all.
If you look at http://schema.org/offers, it says offers is a property of Thing, but I don't see offers listed as a property of Thing at http://schema.org/Thing. What am I misunderstanding here?
Product does define the offers property. If you don’t see the offers property in the first table on that page (under the table heading "Properties from Product"), you are probably affected by a (known) bug. It typically works again when reloading the page later.
offers doesn’t have Thing as domain (but: AggregateOffer, CreativeWork, Event, MenuItem, Product, Service, Trip). If you are referring to the line "Thing > Property > offers", it doesn’t mean that the offers property is defined for/at Thing, it means that the offers property is a Thing. You can ignore that detail. What matters is the domain ("Used on these types") and the range ("Values expected to be one of these types") of a property.
It's perhaps worth highlighting the distinction between "types" and "properties". The vocabulary is a hierarchical taxonomy of the tangible and intangible things around us, which it calls types. In microdata, these use the itemtype attribute.
Properties describe the attributes of and relationships between the types, and in microdata use the itemprop attribute.
So, the type Product has the property offers (it's definitely there, you must be missing it1). A product can offer various things, one of which is the possibility of having some right to own or use it, which is described by the type Offer.
The property offers is indeed a property of Thing, but Thing is at the very top of the taxonomy, i.e. everything the ontology describes is a "thing", tangible or otherwise. So Thing is then broken down into more specific types of things:
Thing
- Intangible
-- Offer
-- Property
--- offers
So offers is a Thing like you and I are things — it's true, but we could be a lot more specific. In this case, offers is a property of the type Property, which in turn is a a more specific type of Intangible, which is a Thing.
1 Image of "offers" property under /Product:
I've just started my journey with REST, so please be patient while anserwing my questions.
I have some doubts how to cope with some situations. For instance, I read that evenry resource/entity should have its own, unique URL. But how to deal with examples like:
There is a list of objects.
Each object is described by some basic information and its state.
Basic info for object is for example its shape, color.
The state of object contains information like position in space, velocity etc.
Both two pieces of information (basic + state) are rather big objects (only examplary properties were introduced).
Now, we have the following questions:
Get all basic info about objects.
Get all object states.
Get basic info of object with ID=2.
Get state of object ID=5.
Get all info of object ID=7.
I tried to solve it in this way:
/rest/objects
/rest/states
/rest/objects/2/basic
/rest/objects/5/state (/rest/states/5)
/rest/objects/7
However, I've some doubts pointed in 4 - it doesn't look like to be correct. There are two ways to access the same information/resource/entity.
How to deal with it?
Isn't the "basic" just part of the resource? It seems not from your description, but you should consider it. In fact, all of "basic" and "state" might just be part of the resource. It's difficult to be authoritative without more information. For instance, how large is "rather big"?
It also doesn't seem like /state should be an independent endpoint, since a state is an integral part of an object, not something that lives on its own.
I might start with something like:
1. GET /objects
2. GET /objects?expand=state
3. GET /objects/2?expand=basic -- or -- GET /objects/2/basic
4. GET /objects/5?expand=state -- or -- GET /objects/5/state
5. GET /objects/7?expand=basic,state
If you need /state to be top level, then you have two options:
2. GET /states -- or -- GET /objects/states
Neither of those are really ideal. It is acceptable to have multiple paths to get to the same resource, as long as there's only one canonical URI for the resource. The issue is that it's harder for the end user to learn APIs that lean heavily on that style. The second style is also confusing. /objects/XXX is a specific object, unless XXX == states? That's a special case for your end user to have to remember.
From a caching point of view it makes sense to have "state" and "basic" in separate resources - "state" resources changes frequently and is thus non-cachable and "basic" changes seldom and should thus be cachable for a long time. If this is your goal, then go ahead, it sure makes sense (and is an often mentioned pattern). But usually, to keep complexity low, both sets of values are combined into one single resource (your "Object" in this case).
Your paths are pretty good, Eric's version is also fine - here is my suggestion:
/rest/objects (all complete objects info)
/rest/objects/basic (all basic info)
/rest/objects/state (all state info)
/rest/objects/7 (single complete object)
/rest/objects/2/basic (single basic info)
/rest/objects/5/state (single state info)
In the end it all boils down to a matter of personal preference as the exact URL doesn't matter much.
See for instance http://soabits.blogspot.dk/2013/10/url-structures-and-hyper-media-for-web.html for a longer discussion on this issue (disclaimer: that's my blog).
resource/entity
Don't confuse these concepts. REST has nothing to do how you store your data, and resources map to entities only by CRUD applications.
I read that evenry resource/entity should have its own, unique URL.
You should read the IRI standard. IRIs are for identifying resources. Without them you cannot tell the server what you want to manipulate.
However, I've some doubts pointed in 4 - it doesn't look like to be
correct. There are two ways to access the same
information/resource/entity.
How to deal with it?
It is up to you. You can choose either of them or both. There is no restriction about how many identifiers a resource can have or what IRI structure to choose.
I would like to know if there is anyone who has implemented the subjectscheme maps of DITA1.2 in their work? If yes, can you please break-up the example to show:
how to do it?
when not to use it?
I am aware of the theory behind it, but I am yet to implement the same and I wanted to know if there are things I must keep in mind during the planning and implementation phase.
An example is here:
How to use DITA subjectSchemes?
The DITA 1.2 spec also has a good example (3.1.5.1.1).
What you can currently do with subject scheme maps is:
define a taxonomy
bind the taxonomy to a profiling or flagging attribute, so that it the attribute only takes a value that you have defined
filter or flag elements that have a defined value with a DITAVAL file.
Advantage 1: Since you have a taxonomy, filtering a parent value also filters its children, which is convenient.
Advantage 2: You can fully define and thus control the list of values, which prevents tag bloat.
Advantage 3: You can reuse the subject scheme map in many topic maps, in the usual modular DITA way, so you can apply the same taxonomies anywhere.
These appear to be the main uses for a subject scheme map at present.
The only disadvantages I have found is that I can think of other hypothetical uses for subject scheme maps such as faceted browsing, but I don't think any implementation exists. The DITA-OT doesn't have anything like that yet anyway.
I'm having a hard time deciphering Scala API documentation.
For example, I've defined a timestamp for use in a database.
def postedDate = column[Timestamp]("posted_date", O NotNull, O Default new Timestamp(Calendar.getInstance.getTimeInMillis), O DBType("timestamp"))
If I hadn't read several examples, of which none were in the API doc, how could I construct this statement? From the Column documentation how could I know the parameters?
I guessed it had something to do with TimestampTypeMapperDelegate but it is still not crystal clear how to use it.
The first thing to note from the scaladoc for Column is that it is abstract, so you probably want to deal directly with one if its subclasses. For example, NamedColumn.
Other things to note are that it has a type parameter and the constructor takes an implicit argument of a TypeMapper of the same parameter type. The docs for TypeMapper provide an example of how to create a custom one, but if you look at the subclasses, there are plenty of provided ones (such as timestamp). The fact that the argument is declared as implicit suggests that there could be one in scope, and if so, it will automatically be used as the parameter without explicitly stating that. If there isn't an implicit in scope that satisfies the requirement, you'll have to provide it.
The next think to note is that a TypeMapper is a trait that extends a function with an argument of a BasicProfile and a TypeMapperDelegate result. Basically what's going on here is the definition of a type mapper is separated from the implementation. This is done to support multiple flavors of database. If look at the subclasses of BasicProfile, it will become apparent that ScalaQuery supports quite a few, and as we know, their implementations are sometimes quite different.
If you chase the docs for a while, you end up at the BasicTypeMapperDelegates trait that has a bunch of vals in it with delegates for each of the basic types (including timestamps).
BasicTable defines a method called column (which you've found), and the intent of the column method is to shield you from having to know anything about TypeMappers and Delegates as long as you are using standard types.
So, I guess to answer your question about whether there is enough information in the API docs, I'd personally say yes, but the docs could be enhanced with better descriptions of classes, objects, traits and methods.
All that said, I've always found that leveraging examples, API docs, and even the source code of the project provides a robust way of getting up to speed on most open source projects. To be quite blunt, many of these projects (including ScalaQuery) have saved me countless hours of work, but probably cost the author(s) countless hours of personal time to create and make available. These are not necessarily commercial products, and we as consumers shouldn't hold them to the same standards that we hold for-fee products. If you find docs inadequate, contribute!
I'm struggling with the size of output files for large Modelica models. Off course, I can protect some objects in order to remove them completely from the result file. However, that gives rise to two problems:
it's not possible to redeclare protected objects
if i want to test my model in detail (eg for a short time period), i need to declare those objects publicly again in order to see their variables
I wonder if there's a trick to set the 'verbosity' of a Modelica model. Maybe what I would like is a third keyword next to public, protected, eg. transparent. Then, when setting up a simulation, I want be able to set the verbosity level to 1, or 2 with the following effect:
1--> consider all transparentelements as protected
2--> consider all transparentelements as public
This effect would propagate to all models and submodels.
I don't think this already exists. But is there an easy workaround?
Thanks,
Roel
As Michael Tiller wrote above, this is not handled the same way in all Modelica tools and there is no definite answer. To give an OpenModelica-specific answer, it's possible to use simulate(ModelName,outputFilter="regex"), to store only the variables that fully match the given regex (default is .*, matching any variable).
Roel,
I know several people wrestling with this issue. At the moment, all of this depends on the tool being used. I don't know how other tools handle filtering of results, but in Dymola you control it (as you point out) by giving the signals special qualifiers (e.g. protected).
One thing I've done in the past is to extend from a model and then add a bunch of output signals for things I'm interested in. Then you can select "Outputs" in Dymola to make sure those get in the results file. This is far from perfect because a) listing everything you want can get tedious and b) referencing protected variables is not strictly allowed (although Dymola lets you get away with it but issues a warning).
At Dassault, we are actively discussing this idea and hope to provide some better functionality along these lines. It isn't clear whether such functionality will be strictly tool specific or whether it will involve the language somehow. But if it is language related, we will (of course) work with the design group to formulate a specification that other tool vendors can support as well.
In SystemModeler, you go to the Settings tab in the Experiment Browswer in Simulation Center. Click on Output on the bottom and select which variables to store.
(The options are state variables, derivatives, algebraic variables, parameters, protected variables and if you mark the Store simulation log-option, you'll get some interesting statistics on events over time and function evaluations, opening another possibility to track down parts of the simulation and model that creates more evaluations)
I am not sure if this helps you, but in Dymola you can go to Simulation->Setup->Output and mark a checkbox saying "Store Protected variables". That way it is possible to declare most variables as protected: during normal simulation they are not stored, but when debugging your model, you just mark that checkbox and they are stored.
Of course that is not the same as your suggested keyword transparent, but maybe it helps a little...
A bit late, but in Dymola 2013 FD01 and later you can select which variables to store based on names (and model names) using the annotation __Dymola_selections, and even filter on user-defined tags - so you could create a tag name "transparent" in the model. See "Matching and variable selections" in the manual.