We are gonna draw a DMN diagram for entities like the image below. Travel entities include a list(many to one relation) of Persons.
There is a problem with designing a DMN with Enterprise Architecture for such a system:
It is not possible to use the data type defined as person in travel and it must be defined in travel. We would like some think like (Person : Person) but as far as I know we haven’t got complex type in EA.
After all we can’t add list data in dataset dialog
Related
In one on my software engineering homework i need to make the class diagram for modelling the problem of develop a system for a public library that can manage its loan service.
In this scenario i have an user, that can loan trough a loan service some library material (like audio dvd, video, text like book or something else).
This is the rapid blueprint:
Now my questions are:
Q1: How can i model the association between user and the loan service? and , exactly, what is the name of this association?
Q2: The loan service class only have one istance, because i think that the service is global for all user, so is correct to modelling this in the cardinality of the association?
Thank's in advance.
When you are to make an information model for the business operations of an organization (in your case, a public library), you have to identify all entity types involved (e.g., users, media types, media items such as books and DVDs, loans, reservations, etc.) and the associations between them (e.g., the class User would be associated with Loan).
But you don't include a class for the organization itself (or its information system) in the model. Consequently, do not include a class for "loan service".
This approach results in an information design model that is the basis for deriving both an OOP class model for defining model classes (also called entity classes) and a database table model (e.g., for defining a MySQL database schema).
The model/entity classes provide the foundation for your app or IS.
Depending on your app development approach (e.g., the chosen framework), you may have to design other classes (e.g., for the user interface), but, compared to the model/entity classes, they are less fundamental.
First time posting here as I was told to seek help from this community if I was ever stuck!!
I was recently introduced to databases this semester and I have a hard time grasping the bridge entity that is meant to erase the many-to-many relationships.
The classic example would be the relationship between STUDENT and CLASS;
where STUDENT can be in many CLASSES and a CLASS can have many STUDENTS.
The M-M relationship is fixed by introducing the ENROLL entity. Here we would read: a STUDENT can ENROLL in many CLASSES, and a CLASS may have many STUDENTS ENROLLED in it, however each STUDENT can be ENROLLED in a CLASS only once.
In my case, I tried to fix a M-M relationship issue between PRODUCT and RAW MATERIAL for a pharmaceutical company by introducing an INGREDIENT entity, which looks like this:
RAW MATERIAL 1----M INGREDIENT M----1 PRODUCT
I am not sure if the bridge works out because I have trouble interpreting it like the STUDENT-CLASS example above.
How would you interpret this?
The concept of "bridge" or "associative" entities came from network data modeling and was a way of handling many-to-many binary as well as ternary and higher relationships. Network data modeling is a simple physical data model based on representing entities as records and relationships as references/pointers.
Since the 1970s, the relational model of data has been developed which uses relations (tables) to record relationships between sets of values (which represent business entities, measurements and labels), allowing for the direct representation of many-to-many relationships and ternary and higher relationships.
The entity-relationship model was an attempt to provide more conceptual structure on top of the relational model, by distinguishing entity relations from relationship relations.
My point with the history is that in modern data modeling, we no longer resolve or erase many-to-many (or ternary or higher) relationships (unless you're using an object-relational mapper or framework based on the network data model). Tables with composite keys, consisting of two or more entity keys, directly represent relationships, and allow us to handle attributes on relationships as well, another feature missing from network data modeling.
In your case, it may be useful to add a Quantity attribute on your Ingredient relationship. The interpretation here is that Raw material refers to a type of material rather than a specific piece or selection of raw material. Students have identity, raw materials generally don't.
Note that pharmaceutical companies may well track specific batches of raw materials.
We have a complex class model of clinical information. It's intended to support model-driven architecture, so the we can't just defer the complexity. But we also need subject matter experts to be able to review it. Is there a way in UML to create "views" like you would in SQL?
In a diagram, you show only classes you want and you get several diagrams to present all points you need.
Your UML model contains all classes, but in a diagram you present only classes you want.
There i a specific UML meta-class for your purpose : Model which inherits from Package.
"A Model is a description of a system, where ‘system’ is meant in the broadest sense and may include not only software and hardware but organizations and processes. It describes the system from a certain viewpoint (or vantage point) for a certain category of stakeholders (e.g., designers, users, or customers of the system) and at a certain level of abstraction. A Model is complete in the sense that it covers the whole system, although only those aspects relevant to its purpose (i.e., within the given level of abstraction and viewpoint) are represented in the Model." p 245
And
" A model captures a view of a physical system. It is an abstraction of the physical system, with a certain purpose. This purpose determines what is to be included in the model and what is irrelevant. Thus the model completely describes those aspects of the physical system that are relevant to the purpose of the model, at the appropriate level of detail." p 273
And it shown like :
But to do like view, meaning to present to user a "public" view of a complex model, you have to use some patterns like :
facade
mediator
I have a language table for 2 fields id and language_name. Can I consider this as a value object?
Ex record: 1 EN
2 DE
3 TR
As soon as these values are immutable, I think I don't need to give them Ids and make it as an entity which represented in database directly.
You can consider them as value object, but you don't have to consider everything in DDD way.
According to Martin Fowler's definition:
When we use a Domain Model, we use it because it contains complicated
domain logic. It can be helpful the classify this domain logic into:
validations: checks that input makes sense and objects are properly
suited for further actions.
consequences: initiating some action that will change the state of the world
derivations: figuring out some
information based on information we already have
ValueObject s are good at validates and derivations.
Language tables, on the other hand, are usually used to solve i18n issues(ui/query conern). Generally speaking, there is no domain logic here.This kind of features are easily implemented in simple CRUD style and better for being so. Consider them in DDD add lots of constraints like only aggregates can be returned by the repository or you could only modify an local entity through it's aggregate. For example, Users edit a product, add english description and deutsch description. One can model product as an aggregate and description as value object, but this does not add much value and somtimes annoying(Now a product cannot be edited by a english editor and a deutsch editor at the same time for concurrent modification on an aggregate).
But what if there is some real domain validations and derivations on the product aggregate? like inventory and pricing. This is where bounded context comes to the play. One can have both an inventory/pricing bounded context modeled in DDD and a product description context modeled in CURD.
I am trying to figure out if it is correct to put in the fields of the particular class a reference to an object/collection that this class is related with.
Let's say I have a class University that aggregates many instances of Student class. When I put on my diagram both classes, I add the relationship of aggregation between them.
And now the question: Can I add in University a field like 'students : Student[]'? Do I have to? Or maybe I must not?
Thanks in advance,
Piotr
Attributes own association properties in UML 2. This is new and it is not always easy to understand the concept. I didn't understand why we need an attribute till I have seen the following demo.
The golden rule is that attributes should be created in order to save association information in the model. I have found an interesting teaching session on association and aggregation in UML 2.
It is a 2m30s flash demo
http://www.download-omondo.com/AggregationAndComposition.swf
The above association creation is for expert level, I mean modeler who wants clean design and clean model as well as perfect metamodel. If you don't care then just create an association at model level and it would do the job but the code generation will not be done. It means that mappings for database will needed to be created at code level later by developers.
To understand the difference between both kinds of associations see this other flash demo at: http://www.download-omondo.com/association.swf
It depends on what you are doing with your model, but generally, you shouldn't have to use an attribute for this, you can use an association instead. Associations are able to contain more information that attributes, such as whether they are composite or shared, which ends are navigable, multiplicity on each end, named endpoints, etc.
One benefit of associations is that one association can actually represent a property on each class it is connected to, while an attribute only represents a property on the class it belongs to.
So, in your case, University has Students, so you'd draw an association from University to Student, naming each endpoint and setting the multiplicity correctly.
Now when you go to generate code from your model, just be sure to take into account associations as well as attributes. This way you won't need to add the properties both as attributes and associations, just as associations. I have a few diagrams I've tested this approach with, generating sql and php code from the xmi via an xsl transform, and it works quite well... if you'd like more details I can dig it up.
There are 3 types of relations : association, aggregation and composition. composition is a specialization of aggregation, aggregation is a specialization of association.
Using one or the other depends on the phase of your analysis. You could just use association in first draft and then refine it later to aggregation or composition, the difference with aggregation is that a student had no meaning out of one University Universe. If there are several universities instances, it would be aggregation rather.
If you use relations, there's no need to and you shouldn't add students[] because it is redundant. And if you do that you lose the semantics of the 3 types of relations.