Telos' structurally object-oriented framework generalizes earlier data models and knowledge representation formalisms, such as entity-relationship diagrams or semantic networks, and integrates them with predicative assertions and temporal information. This combination of features seems to be particularly useful in software information applications such as requirements modeling and software process control. A formal description of Telos can be found in [MBJK90, JEUS92]. The following example is used throughout this section to illustrate the language:
company has employees, some of them being managers. Employees have a name and a salary which may change from time to time. They are assigned to departments which are headed by managers. The boss of an employee can be derived from his department and the manager of that department. No employee is allowed to earn more money than his boss.
This section is organized as follows: first, the frame and network representation of the Telos language is explained. Then, the predicative sublanguage for deductive rules and integrity constraints are presented. Subsection 2.3 presents a declarative query language which introduces queries as classes with optional predicative membership specification.