P. Fraternali et L. Tanca, A STRUCTURED APPROACH FOR THE DEFINITION OF THE SEMANTICS OF ACTIVE DATABASES, ACM transactions on database systems, 20(4), 1995, pp. 414-471
Citations number
61
Categorie Soggetti
Computer Sciences","Computer Science Information Systems","Computer Science Software Graphycs Programming
Active DBMSs couple database technology with rule-based programming to
achieve the capability of reaction to database (and possibly external
) stimuli, called events. The reactive capabilities of active database
s are useful for a wide spectrum of applications, including security,
view materialization, integrity checking and enforcement, or heterogen
eous databases integration, which makes this technology very promising
for the near future. An active database system consists of a (passive
) database and a set of active rules; the most popular form of active
rule is the so-called event-condition-action (EGA) rule, which specifi
es an action to be executed upon the occurrence of one or more events,
provided that a condition holds. Several active database systems and
prototypes have been designed and partially or completely implemented.
Unfortunately, they have been designed in a totally independent way,
without the support of a common theory dictating the semantics of ECA
rules, and thus often show different behaviors for rules with a simila
r form. In this article we consider a number of different possible opt
ions in the behavior of an active DBMS, based on a broad analysis of s
ome of the best known implemented systems and prototypes. We encode th
ese options in a user-readable form, called Extended EGA. A rule from
any existing system can be rewritten in this formalism making all the
semantic choices apparent. Then an EECA rule can be automatically tran
slated into an internal (less readable) format, based on a logical sty
le, which is called core format: the execution semantics of core rules
is specified as the fixpoint of a simple transformation involving cor
e rules. As an important premise to this research, a semantics for dat
abase updates and transactions has also been established, with respect
to a notion of state that comprises both data and events. The article
also presents an extensive bibliography on the subject of active data
bases.