We present an exception handling facility suitable for languages used to implement database-intensive Information Systems. Such a mechanism facilitates the development and maintenance of more flexible software systems by supporting the abstraction of details concerning special or abnormal occurrences. We consider the type constraints imposed by the schema as well as various semantic integrity assertions to be normalcy conditions, and the key contribution of this work is to allow exceptions to these constraints to persist. To achieve this, we propose solutions to a range of problems, including sharing and computing with exceptional information, exception handling by users, the logic of constraints with exceptions, and implementation issues. We also illustrate the use of exception handling in dealing with null values, estimates, and measurements. Keywords and phrases: semantic integrity, violations of type constraints, exception handling, accommodating exceptions, conceptual models CR ...

Galileo, a programming language for database applications, is presented. Galileo is a strongly typed, interactive programming language designed specifically to support Semantic Data Model features (classification, aggregation and specialization) as well as abstraction mechanisms of modern programming languages (types, abstract types and modularization). The main contributions of Galileo are: a) the proposal of a flexible type system to model database structure and semantic integrity constraints; b) the inclusion of type hierarchies to support the specialization abstraction mechanism of Semantic Data Models. c) the proposal of a modularization mechanism to structure data and operations into interrelated units; d) the integration of the abstraction mechanisms into an expression based language that allows an interactive use of the database without resorting to a new stand alone query language. Galileo will be used in the immediate future as a tool for database design and, in the long term, as a high level interface for DBMSs. data types; data types and structures; H.2.1 [Database Management]: Logical Design- data models; schema and subschema; H.2.3 [Database Management]: Languages- data description languages (DDL); data manipulation languages (DML); query languages

In a class hierarchy, a “role set ” is t,he set of classes where an object may reside simultaneously. A “migration pattern ” is a sequence of role sets. A “migration inventory, ” which is a set, of migrat,ion patterns, is viewed as a dynamic const,raintm on ohjrct migration. A set of transact ious is “sound ” wrt a11 inventory if it. generates only pat.t.t~rns in the invrntory; “complete ” if all pat,terns in the invent,ory can be generated. An initial stucly on characterizing migration inventories of transact,ions is presented. Three update languages are considered: SL which contains five operat,ors, CSL+ which ext rn(ls SL wit.h posit.ivc conditionals, and CSL which allows hot,h positive and negative condit.ionals. Four kinds of invent.orics are studied based on ln~znrss and znj~~,rtl~ntr s/art. It is shown that inventories produced by SL t,ransactions are regular and every regular inventory can be generated by SL transactions. Soundness and complet,eness for SL t,ransactions are decidahlt3. lnvc\llt,orics gpnrrated by CSL (CSL+) t,ra.nsactions arc r.e‘. and every r.e. inventory can be generat,rd by (:SL+ (CSL) transa.ctions under nonimmediate st,art,. It is also show t,hat, every r.e. immediate-start invent,ory can be obtained by a left quotient, of t,he invent,ory of CSL+ (CSL) transactions hy a regular seb. The exact, charact#erizat.ions are open. However, cvrry contrxl-frcr srt can be generat,ed. Soundness and rmllplPt~enms for ($1, (CSL+) t,ransa.ctions are undecidahlr. 1

A computer system which stores, retrieves and manipulates information about some portion of the real world can be viewed as a model of that domain of discourse. There has been considerable research recently on languages which allow one to capture more of the semantics of the real world in these computerized Information Systems-- research which has variously been labelled as Semantic Data Modeling, Semantic Modeling or Conceptual Modeling. This review paper presents a list of the features which appear to distinguish these languages from those traditionally used to describe and develop database-intensive applications, and considers the motivation for these features as well as the potential advantages to be gained through their use. The paper, which is intended for those familiar with current data processing practices, also compares in greater detail four programming languages which incorporate semantic modeling facilities, and discusses some of the methodologies and tools for Information System development based on these languages.