Software Engineering – Domain Modelling


What is Domain Modelling?

Domain Modelling is a way of representing the context  in which the software must operate – to understand the software better. However, one must remember that you’re not modelling the software to be built!

A better description would be:

A Domain Model in Software Engineering can be thought of as a conceptual model of a system which describes the various entities involved in that system and their relations.

http://en.wikipedia.org/wiki/Domain_model

 

 

Domain Modelling 101

  • Go through the available data sources; such as the original description; Use Cases; Glossary etc etc. With this, you must then identify possible Domain Classes (noun phrases)
  • Identify basic relationships between the domain classes.
  • Add addition key attributes
  • Pay attention to the relationships, like names and multiplicities – it is very important that these are correct!

Domain Modelling Example

Now for the moment you’ve all been waiting for, an example! 😀 Sadly a Domain Model doesn’t have any stick people in it, so there’ll be no awesome stick people of awesomeness 😦

Lets say we have the following information for a basic Student Library System:

Courses may have recommended items of Reading Material, which may be either complete Books or individual Chapters. Items of Reading Material may also allows a user or floppy for every NFA there is i for for have Reviews associated with them.

Now with this we need to identify 5 classes, can you see what they are?

Hint: i cheated a little, they’re in italics…. 😛

So, yeah… we have the 5 classes of:

  1. Courses
  2. Reading Material
  3. Books
  4. Chapters, and
  5. Reviews

And with this, this is what the Domain Model looks like:

BookDM-fixed

 

Before I start to explain what this shows, lets explain the arrows and numbers:

  •  DMline  This is the first thing. This – obviously – is a line. When we see a line connecting 2 classes together this shows us that these 2 classes are related. The text that lays on the line, ie “provides”, says that Course is related to Reading Material as a “Course provides Reading Material”.
  • DMarrow An arrow implies a relation of inheritance. So for the diagram above, its should be obvious that a Book will inherit some methods from Reading Material. A more better example of this could be if we thought of this in a Java/C++ sense. For example, we create a Person Class and then create a Student Class, a Student will inherit methods (etc) from Person, such as getAge() and getHeight() , as well as name and age etc etc.
  • DMcontain This is a line with a funny looking diamond thing on the end. What this states is that class ‘A’ contains class ‘B’. For example, above we say that a Book contains Chapters – which is obviously true, else it would really be a book…
    Another example would be if we had the classes Wallet and Money. So we could have Wallet => contains => Money.
  • The final one is the numbers; so (0, 1, *, 0..* and 1..* and many more). What these state is a relation such as one-to-one, or one-to-many. In the example above we have these numbers on the contains relation for Books and Chapters. So we say that a one (1) Book contains one or more (1..*) Chapters.

    Alternatively we can also say that one (1) Course provides zero or more (0..*) Reading Material.

    As a note, remember that we can only use these numbers on plain relation lines and contains relations. we do NOT use them on inheritance relations! 🙂

And i think that’s it for Domain Models 😀 , sorry for doing this one a little late, i had some issues with the diagram above. However, many thanks to James Bedford, Daniel Lyon 😀

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About Badgerati
Computer Scientist, Games Developer, and DevOps Engineer. Fantasy and Sci-fi book lover, also founder of Cadaeic Studios.

2 Responses to Software Engineering – Domain Modelling

  1. Pingback: Software Engineering – The Class Model « Computer Science: Source

  2. Aysha Rasheed Ahmed says:

    this is a v good example realy….. good work ;

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