A_OCL : A Pure Java Replacement for OCL

OCL (Object Constraint Language) is the standard constraint language for MDE. Personally, I never liked it because it had the look and feel of a "hacked" language; it was not elegant nor simple.

A_OCL is a pure-Java replacement for OCL. It is literally a Java package that supports the operations and almost matches the syntax of OCL that is generated directly from a Violet class diagram or a CDSchema file. Both are documented in this manual and how to transform these inputs into an A_OCL package. Here is the table of contents for this document:

Violet Class Diagrams
Converting a Violet Class Diagram into an A_OCL package

CDSchema files
Converting a CDSchema file into an A_OCL package

A_OCL examples

Violet Class Diagrams

A Violet class diagram can be used to specify an A_OCL package. Here are the rules for creating Violet Class diagrams.

Abstract classes are indicated in Violet by their name: "Abs_X" denotes class X is abstract. The A_OCL package will produce a class "abstract class X" as a result. The figure below will produce an abstract class with name "A"; it will have (by default String) fields with names r, s, and t.
Violet associations must be of one of 4 kinds:

BLACK_DIAMOND -- an association has one end with a BLACK_DIAMOND and the other end with nothing; roles (x,y below) must be supplied on both sides and so too a middle label (M, below).
DIAMOND -- an association has one end with a DIAMOND and the other end with nothing; roles (x,y below) must be supplied on both sides, and so too a middle label (M, below).
NM -- an association has no cardinality end designators (BLACK_DIAMOND) or (DIAMOND) on either end; roles (x,y below) must be supplied on both sides AND that a middle label, to indicate the name of a manufactured "association" class must be supplied.
TRIANGLE --- a Violet association encodes an inheritance relationship the TRIANGLE indicator at the super-class end and nothing at the other end; no roles can be used.

Looped associations (that start and end at the same class) are permitted and follow the above rules for (a)-(c). The figure below shows a diamond loop association, which has roles and a middle label:

Attributes should be typed; if no type is specified "String" is assigned by default. If "N" is given as an attribute name (i.e., N is surrounded by quotes), N is a quoted string (and all of its values must be quoted strings). If N is given by itself (without quotes), its values must be non-quoted --- essentially meaning an Java identifier. An attribute with name N and primitive type T is written (on a separate line) as N:T. MDELite currently supports the following primitive types:

int
float
double
bool

The figure below shows an example of each attribute:

Converting a Violet Class Diagram into an A_OCL Package

Use the following tool to create an allegory package.

> java MDL.V2Aocl

CDschema Files

A cdschema file is an intermediate representation of a class diagram. It is a purely textual specification. Consider the class diagram to the below left and its cdschema specification to the right:

classDiagram I22.

table(Emp,[id,name,age:int]).
table(Div,[id,name,city]).
table(SuperEmp,[degree:int]).
table(SuperDiv,[degree:int]).

subtable(Div,[SuperDiv]).
subtable(Emp,[SuperEmp]).

assoc(Emp,employs,NM,Div,worksIn,In).

A cdschema specification:

starts with a declaration 'classDiagram X.' where X is the name of the diagram.
a sequence of one or more table definitions, exactly like those specified in a dbase schema, except only attributes of primitive types are permitted.
a sequence of zero or more subtable definitions, exactly like those specified in a dbase schema.
a sequence of zero or more association definitions.

The only declaration that is in some sense new is an association declaration. The order in which tables are listed is important. Look at the following figure (a), which shows a Violet association and how it is mapped to an association declaration (b).

For the case of an NM association, because it is symmetrical, Emp or Dept could have been listed first, followed by its role label, followed by its association type (NM in this case), followed by a table (Dept) and its role (worksin), followed by the middle label (Job) which will become the name of an association class.

A more typical association is below. The first table listed is at the BLACK_DIAMOND or DIAMOND end of an assoc declaration. The remaining parameters follow.

Converting a cdschema File into an A_OCL package

Use the following tool to create an allegory package.

> java MDL.V2Aocl

AOCL Examples

Consider the following class diagram (right) and its cdschema (left) as the basis for our AOCL examples.

Now consider the following database:

---eee---

Here is a sequence of queries:

AOCL : A Pure Java Replacement for OCL