Multiple version management of hypothetical databases

This paper presents a Hypothetical Storage Server for an experimen­tal design database system. The storage server provides unified manage­ment of historical versions and hypothetical versions of objects in a design database. The extension of each database object is man.aged as a tree of multiple distinct representatives. One branch of the tree is designated as the primary branch, and its current representative is the primary version of the object. All other branches are considered hypothetical. A new branch in the tree is started when a new hypothetical version is derived from an existing representative. Hypothetical versions can be derived from any representative of the object, including prior versions of either the primary branch or a hypothetical branch. A branch grows when the current representative of the branch is updated. Both the primary version of the object and current versions of its hypothetical branches can be updated. Updating the primary version is equivalent to updating the object. An update to any other branch of the tree is a hypothetical update of the object. Updates to the primary version of the object must be serializable, but derivation of hypothetical versions is not subject to such a constraint. Thus only write-write conflicts are subject to constraint, and conflicting updates can always be accepted by creating new hypothetical versions

FORMAL SEMANTICS FOR TIME IN DATABASES

The concept of an historical database is introduced as a tool for modelling the dynamic nature of some part of the real world. Just as first-order logic has been shown to be a useful formalism for expressing and understanding the underlying semantics of the relational database model, intensional logic is presented as an analogous formalism for expressing and understanding the temporal semantics involved in an historical database. The various components of the relational model, as extended to include historical relations, are discussed in terms of the model theory for the logic ILs, a variation of the logic IL formulated by Richard Montague. The modal concepts of intensional and extensional data constraints and queries are introduced and contrasted. Finally, the potential application of these ideas to the problem of Natural Language Database Querying is discussed.Information Systems Working Papers Serie