An Aocl Example
March 5, 2020

Although OCL is a complex language, at its core is an elegant sublanguage of Relational Algebra, written in an OO syntax, with special names for right-semijoins (a.k.a. association traversals). This reduced language is Aocl, which can be implemented in pure Java 8.0. Given a textual specification of a class diagram, a tool generates the Aocl package for that class diagram to write metamodel constraints or to write model transformations. This example previews the Aocl toolset. A class diagram is given with its generated Aocl Java package, and with Java programs that illustrate/execute Aocl expressions.

Installation

Copy the files of this distribution into a fresh directory DIR. Place the following Jars In the DIR/dist/ directory onto your Java CLASSPATH:

DIR/dist/MDELite9.1.jar
DIR/dist/Meta4.0.jar

On windoze this is:

> set CLASSPATH=%CLASSPATH%;DIR\dist\MDELite9.1.jar;DIR\dist\Meta4.0.jar

On Macs, try:

> export CLASSPATH=$CLASSPATH:DIR\MDELite9.1.jar:DIR\Meta4.0.jar

Also, make sure that dot (.), the current directory, is also on your CLASSPATH! To compile the source code of this distribution type:

Dir> java *.java

Please note: by doing the above, you have installed the binary version of Aocl.

Overview

I created an example for you to try Aocl. It has all you need to pose and execute queries and constraints on the class diagram below. The diagram has 3 classes:

each Emp(loyee) has a name and an integer age;
each Dept (department) has a name and a quoted string city ("New York") where blanks count;
each Div(ision) has a name.

Further, there are 3 associations:

Anc encodes ancestry information: each Emp has 0..* number of Emp parents and 0..* Emp children;
Job encodes employment information: each Emp worksin 0..* Depts and each Dept employs 0..* Emps;
DD encodes that each Dept belongs to precisely 1 Div.


% a line-comment begins with %

classDiagram Alleg.

table(Emp,[name,age:int]).
table(Dept,[name,'city']).
table(Div,[name]).

assoc(Anc,Emp,parOf,BLANK,Emp,chldOf,BLANK).
assoc(Job,Emp,employs,BLANK,Dept,worksin,BLANK).
assoc(DD,Div,inDiv,BLACK_DIAMOND,Dept,hasDept,BLANK).

To the right of the diagram is a textual specification of the diagram itself. Briefly:

The document begins with the name of the class diagram, in this case "Alleg".
There is a table declaration for each table. In Prolog format, it is the name of the table followed by a list of its fields. A field can be:

just a name, eg "name". It has the default type "str" for string, much like a Prolog name;
a quoted name, 'city'. It has the default type "qstr" for quoted string where blanks are important; or it is
a name:type spec. Both the attribute name and type are given. Primitive types are {int,str,qstr,bool}.

There is an assoc declaration for each association:

the name of the association (Job);
the name of one class followed by the role name visually adjacent to it; (Emp,employs);
the kind of association end (0..* = BLANK, 0..1 = DIAMOND, 1..1 = BLACK_DIAMOND), e.g. "BLANK";
do the same for the other association end (Emp,chldOf,BLANK); and
the first class listed in an association has the greatest "strength": BLACK_DIAMOND > DIAMOND > BLANK.

This textual specification is called a CDSpec (for Class Diagram Specification), and is stored in a file named, for example, alleg.cdspec.pl

files usually have 3-part names: the filename ("alleg"), the specification type (cdspec.pl).

Note: there is some constraint checking in CDSpec. It could be improved, like having a CDSpec conformance program. On my TODO list.

Meta4 Tool

A Java tool, Meta4, translates a CDSpec file into a Java package that implements tables, tuples, and databases and operations on them. You have Meta4 in this distribution. If you want to see what it does, type:

> java M4.Meta4 alleg

or

> java M4.Meta4 alleg.cdspec.pl

The contents of directiory Allegory/Alleg will be generated. (I've already given it to you in this distribution, so you can skip this step. Note: the first letter of a package name is capitalized by Meta4). There is a Java class file for:

each tuple type (Emp, Dept, Div, Job, Anc);
each table type (EmpTable, DeptTable, DivTable, JobTable, AncTable);
an Alleg database (whose instances are Alleg databases);
an Alleg database schema

Of course, you'll need a database (a relational database encoding of an object-diagram) on which you are to execute your queries. I've provided one x.alleg.pl (x is the name of the database whose schema is alleg.schema.pl).

Running Aocl

3 programs that You can edit and run 3 Java programs:

Driver -- gives a good cross-section of Aocl queries and constraints. Looking further, you can uncomment some calls to MoreQueries and MoreConstraints;
AncestryEx -- gives a few queries to explore ancestry relationships; and
GroupByTests -- gives a few group-by queries.

Run any of the above (like Driver) without arguments:

> java Driver

All output is to Standard.out. A bash script to clean the directory is clean.script.

Have Fun! Send complaints and comments to batory@cs.utexas.edu.

An Aocl ExampleMarch 5, 2020

Installation

Overview

Meta4 Tool

Running Aocl

An Aocl Example
March 5, 2020