Antonio Albano

GALILEO: a strongly-typed, interactive conceptual language

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 the abstraction mechanisms of modern programming languages (types, abstract types, and modularization). The main contributions of Galileo are (a) a flexible type system to model database structure and semantic integrity constraints; (b) the inclusion of type hierarchies to support the specialization abstraction mechanisms of semantic data models; (c) a modularization mechanism to structure data and operations into interrelated units (d) the integration of abstraction mechanisms into an expression-based language that allows 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.

NESTING TWO-DIMENSIONAL SHAPES IN RECTANGULAR MODULES

A problem of relevant interest to some industries is that of optimum two-dimensional layout. In this problem, one is given a number of rectangular sheets and an order for a specified number of each of certain types of two-dimensional regular and irregular shapes. The aim is to cut the shapes out of the sheets in such a way as to minimize the amount of waste produced. A two-stage solution is proposed in which the problem is converted from one of placing irregularly shaped pieces to one of allocating rectangular modules. The clustering algorithm used in the first stage to produce rectangular modules is presented and the results obtained when it was applied to some typical layout problems are described.

Fibonacci: a programming language for object databases

Fibonacci is an object-oriented database programming language characterized by static and strong typing, and by new mechanisms for modeling data-bases in terms of objects with roles, classes, and associations. A brief introduction to the language is provided to present those features, which are particularly suited to modeling complex databases. Examples of the use of Fibonacci are given with reference to the prototype implementation of the language.

Yet another query algebra for XML data

XML has reached a widespread diffusion as a language for representing nearly any kind of data source, from relational databases to digital movies. Due to the growing interest toward XML, many tools for storing, processing, and querying XML data have appeared in the last two years. Three main problems affect XML query processing: path expression evaluation, nested query resolution, and preservation of document order. These issues, which are related to the hierarchical structure of XML and to the features of current XML query languages, require compile-time as well as run-time solutions. This paper describes a query algebra for XML data. The main purpose of this algebra, which forms the basis for the Xtasy database management system, is to combine good optimization properties with a good expressive power that allows it to model significant fragments of current XML query languages; in particular explicit support is given to efficient path expression evaluation, nested query resolution, and order preservation.

A method to improve two-dimensional layout

Abstract A graphics problem of great interest to industry is that of optimum two-dimensional layout. An operator is given a number of rectangular sheets and an order for a specified number of certain types of two-dimensional shapes. The objective is to cut the shapes out of the sheets in such a way as to minimize the amount of waste produced. A system is proposed where a tentative solution is automatically generated and then interactive improvements are allowed by a conversational display unit. The design criteria, the structure and the main features of the system are illustrated.

An Overview of Sidereus: A Graphical Database Schema Editor for Galileo

Sidereus is a workstation based graphical tool to edit a Galileo database schema using a diagrammatic notation. Several tools to manipulate a graphic representation of a database schema exist as commercial products or research prototypes, but the novel aspects of this proposal lie in the fact that the graphical editor is used to model a database using a semantic data model, to deal with complex objects with the values of attributes definable using the rich type system of Galileo, a database language that supports the abstraction mechanisms of semantic data models. Moreover, schemes designed with Sidereus are translated automatically in Galileo code, executable on the same workstation.

View operations on objects with roles for a statically typed database language

To deal with the evolution of data and applications and with the existence of multiple views for the same data, the object data model needs to be extended with two different sets of operations: object extension operations, to allow an object to dynamically change its type; and object viewing operations, to allow an object to be seen as if it had a different structure. Object extension and object viewing operations are related in that they are both identity-preserving operations, but different in that object extension may modify the behavior of the original object while object viewing creates a new view for the original object without modifying its behavior. A set of object viewing operations is defined in the context of a statically and strongly typed database programming language which supports objects with roles, and the relationships with object extension and role mechanisms are discussed. We then show how the object viewing operations can be used to give the semantics of a higher level mechanism to define views for object databases. Examples of the use of these operations are given with reference to the prototype implementation of the language Galileo 97.

A typed text retrieval query language for XML documents

XML is nowadays considered the standard meta-language for document markup and data representation. XML is widely employed in Web-related applications as well as in database applications, and there is also a growing interest for it by the literary community to develop tools for supporting document-oriented retrieval operations. The purpose of this article is to show the basic new requirements of this kind of applications and to present the main features of a typed query language, called Tequyla-TX, designed to support them.

Persistent Object Systems

The problem of clustering objects onto units of secondary storage is both important and difficult. It is related to the problem of allocating mes to nodes in a network and both problems have been shown to be NP complete. This paper discusses a workbench for evaluating heuristics to solve the object clustering problem and the somewhat surprising result that real problems can sometimes be solved quite easily.

The type system of Galileo

Galileo is a conceptual language, i.e., a programming language for database applications which supports both the abstraction mechanisms of modern programming languages (data types, abstract data types, modules) and the abstraction mechanisms of semantic data models (SDM) (classification, aggregation, generalization). Unlike other conceptual languages, Galileo is a strongly typed language which exploits the benefits of data types for modeling the abstract knowledge of information systems. The type system of Galileo has been designed to deal with the intensional aspects of the SDM abstraction mechanisms, while the class and subclass mechanism is provided to deal with the extensional aspects. The following relevant features of the type system will be emphasized: type hierarchies and declarative overloading, which provide a kind of polymorphism in a strongly typed language whose range of applications goes beyond the scope of conceptual modeling.