Explanation
Services are meant to expose functionality and data from a context, to let users or information systems interact with the system by creating, reading, updating, and deleting data.
Note: The service definition must be outside a pattern
The following figure is an example of a user interface, which shows the name, status, e-mail and co-workers of a person called "J. Lovell".
The specification of this user interface is given in the following service definition:
To understand this fragment, take notice of:
The name of this service is Person. This name immediately follows the keyword INTERFACE.
The term following the colon, I[Person], is the interface term of this service.
You can create structure in a service by nesting. Here is an example:
The specification of this service is given in the following code fragment.
Notice the following features:
1. The structure of a service is hierarchical. It consists of boxes within a box. This is because a field term may be followed by a BOX with a list of subservices. Without it, it is just a field term. 2. When a field term is followed by a BOX, every atom in the codomain of the field term is displayed in a box of its own on the screen. That box behaves like a service with the field term serving as interface term of that subservice. 3. By this mechanism, the hierarchical structure of the entire service translates directly to the hierarchical structure of the web-page in which it is displayed. 4. The source concept of a field term must match with the target concept of the field term outside the box.
5. The target concept of a field term that has a box, must match with the source concepts of each field inside that box.
Especially in more complicated services, you will find it nice to adapt the layout of the fields in the user interface. For this purpose, you can substitute the word BOX by COLS, ROWS, or TABS, as in the following code fragment. Note that these annotation have no meaning other than to change what the user interface looks like.
Notice the effect that these changes have on the user interface.
Notice the following features:
1. The keyword TABS turns the box into a tabulated layout.
2. The keyword COLS turns the layout 90 degrees into columns.
3. The keyword ROWS is default for any box. It does not change the effect of BOX.
Compile and run the script . Start by reproducing everything that is shown above. It is quite likely that you will be trying out your own ideas before you get to the end... Have fun!
What have you learned?
After finishing your assignment, you have learned:
to explain how a service definition is displayed on the screen of a user.
to predict which data items a service applies to, if you know which pairs are in an interface term.
to predict which data items are displayed, if you know which pairs are in a field term.
