Introduction to the Object Constraint Language (OCL)
Overview
The Object Constraint Language (OCL) is a formal language used to express
constraints and navigation within Unified Modeling Language (UML) models.
Developed in  1997  by IBM it is now managed by the Object Modeling Group (OMG)
and is included as part of the UML specification.
OCL is required because a class model, by itself, is incomplete as means of
specifying requirements of the classes at runtime. In the past the extra definition
applied to UML diagrams was in the format of natural language. However, as this is
open to ambiguous interpretation and not executable as code, it failed to address it
primary requirement of simplifying and clarifying the class model.
OCL provides a simple language that can be used to express boundaries for class
instances at runtime (constraints) as well as provide a clear means to navigate the
model.

Prolog is a powerful programming language, based on logic, that originated 
and matured in Europe. This paper aims to show that Prolog is becoming one of 
the key tools for the entire application development community. First explained 
is how the unique properties of Prolog give it many advantages over classical 
languages. Then we show that the language is sufficiently mature technically so 
that numerous industrial Prolog products are now available. In particular, IBM 
offers the Systems Application Architecture (SAA TM ) AD/Cycle Prolog product 
family, which provides a combination of logic programming and object 
programming facilities. Many industrial applications are written in Prolog. 
Examples of  15  outstanding operational applications, developed by IBM or major 
IBM customers, are presented. There is a potential for future growth in the 
types of applications enabled by improving the language. The simplicity and 
elegance of the theoretical basis of Prolog allow a number of extensions to be 
defined. Here, three European projects are briefly presented. In conclusion it 
is shown that Prolog, possibly extended in many directions, is one of the tools 
that could help solve the long-standing quality and cost problems in 
application development...

Prolog is a powerful programming language, based on logic, that originated 
and matured in Europe. This paper aims to show that Prolog is becoming one of 
the key tools for the entire application development community. First explained 
is how the unique properties of Prolog give it many advantages over classical 
languages. Then we show that the language is sufficiently mature technically so 
that numerous industrial Prolog products are now available. In particular, IBM 
offers the Systems Application Architecture (SAA TM ) AD/Cycle Prolog product 
family, which provides a combination of logic programming and object 
programming facilities. Many industrial applications are written in Prolog. 
Examples of  15  outstanding operational applications, developed by IBM or major 
IBM customers, are presented. There is a potential for future growth in the 
types of applications enabled by improving the language. The simplicity and 
elegance of the theoretical basis of Prolog allow a number of extensions to be 
defined. Here, three European projects are briefly presented. In conclusion it 
is shown that Prolog, possibly extended in many directions, is one of the tools 
that could help solve the long-standing quality and cost problems in 
application development...