TOS: a temporal object system
Abad Ali Shah · 1992
In many engineering applications, changes to the state and structure of an object need to be maintained over a period of time. Existing object-oriented data models allow such changes in the state (referred to as Version Management) and structure (referred to as Schema Evolution) of an object. However, when the structure changes, the old structure is replaced by the new one. We proposed a Temporal Object System (TOS) which maintains changes to both the structure and the state of an object. Objects in TOS are referred to as Temporal Objects and are allowed to evolve over time. A family is a collection of temporal objects which share a common set properties: root of family (ROF). We define an aggregation of a set of simple families as a complex family and a temporal object of the complex family is called a temporal complex object (TCO). A temporal object that can also be defined by using local knowledge of a family is referred to as an offstage object. Offstage objects and temporal objects can replace and refresh their knowledge through a process called renovation. We discuss the renovations of both temporal complex objects and offstage objects and enumerate their temporal parameters (i.e. time-span, life-span and life-sequence) after renovation. The available knowledge sharing mechanisms, inheritance and delegation, are not suitable for a temporal system, therefore, we propose a knowledge sharing mechanism Share-kno and give it a formal model. We prove that Share-kno is more knowledgeable than the inheritance and delegation models which are proposed by Stein. We also give the syntax of the data definition and data manipulation languages (DDL & DML) for TOS. A data manipulation language, temporal object-oriented query (TO$\sp2$L), is proposed which is a super-set of the relational query language SQL. It can answer temporal and non-temporal queries of a TOS from a stage level to system level. In the end, we propose two future research directions. The first direction is implementation of a TOS, and the second is to provide a mathematical background to TOS. To make TOS more formal, the mathematical tool category theory is suggested. This can give a mathematical foundation to this research.