Active database systems require facilities to specify triggers that fire when specified events occur. We propose a language for specifying composite events as eveti expressions, formed using event operators and events (primitive or composite). An event expression maps an event history to anothe-r event history that contains only the events at which the event expression is “satisfied ” and at which the trigger should 6re. We present several examples illustrating how quite complex event specifications are possible using event expressions. In addition to the basic event operators, we also provide facilities that make it easier to specify composite events. “Pipes ” allow users to isolate sub-histories of interest. “Correlation variables ” allow users to ensure that different parts of an event expression are satisfied by the same event,

. In this paper we de#ne the concept of self-maintainable views # these are views that can be maintained using only the contents of the view and the database modi#cations, without accessing any of the underlying databases. We derive tight conditions under which several types of select-project-join are self-maintainable upon insertions, deletions and updates. Self-Maintainability is a desirable property for e#- ciently maintaining large views in applications where fast response and high availability are important. One example of suchanenvironment is data warehousing wherein views are used for integrating data from multiple databases. 1 Introduction Most large organizations have related data in distinct databases. Many of these databases may be legacy systems, or systems separated for organizational reasons like funding and ownership. Integrating data from such distinct databases is a pressing business need. A common approach for integration is to de#ne an integrated view and...

In this paper, we motivate and present a data model for conceptual design of structural and behavioural aspects of databases. We follow an object centered design paradigm in the spirit of semantic data models. The specification of structural aspects is divided into modelling of object structures and modelling of data types used for describing object properties. The specification of object structures is based on an Extended Entity--Relationship (EER) model. The specification of behavioural aspects is divided into the modelling of admissible database state evolutions by means of temporal integrity constraints and the formulation of database (trans)actions. The central link for integrating these design components is a descriptive logic-- based query language for the EER model. The logic part of this language is the basis for static constraints and descriptive action specifications by means of pre- and postconditions. A temporal extension of this logic is the specification language for tem...

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Abstract. The correctness of the data managed by database systems is vital to any application that utilizes data for business, research, and decision-making purposes. To guard databases against erroneous data not reflecting real-world data or business rules, semantic integrity constraints can be specified during database design. Current commercial database management systems provide various means to implement mechanisms to enforce semantic integrity constraints at database run-time. In this paper, we give an overview of the semanticintegrity support in the most recent SQL-standard SQL:1999, and we show to what extent the different concepts and language constructs proposed in this standard can be found in major commercial (object-)relational database management systems. In addition, we discuss general design guidelines that point out how the semanticintegrity features provided by these systems should be utilized in order to implement an effective integrity enforcing subsystem for a database. Keywords: Semanticintegrity constraints – SQL:1999 – Object-relational databases – Constraint enforcement

This paper describes a model that integrates the execution of triggers with the evaluation of declarative constraints in SQL database systems. This model achieves full compatibility with the 1992 international standard for SQL (SQL92). It preserves the set semantics for declarative constraint evaluation while allowing the execution of powerful procedural triggers. It was implemented in DB2 for common servers and was recently accepted as the model for the emerging SQL standard (SQL3). 1 Introduction Active databases are taking a prominent role in commercial database applications [6, 30, 29, 13]. With client/server solutions, applications are being developed by small, autonomous groups of developers with narrow views of the overall enterprise; the enterprise information system is very vulnerable to integrity violations because it lacks strict enforcement of the enterprise business rules. Active data proactively monitors events and, without user intervention, protects its own integrity...

An XML-to-relational mapping scheme consists of a procedure for shredding XML documents into relational databases, a procedure for publishing databases back as documents, and a set of constraints the databases must satisfy. In previous work, we discussed two notions of information preservation for mapping schemes: losslessness, which guarantees the complete reconstruction of a document from a database; and validation, which guarantees that every update to a database corresponding to a valid document results in a database corresponding to another valid document. Also, we described one information preserving mapping scheme, called Edge ++, and showed that, under reasonable assumptions, lossless and validation are both undecidable. This leads to the question we study in this paper: how to design information-preserving mapping schemes. We propose to do it by starting with a scheme known to be information preserving (such as Edge ++) and applying to it equivalencepreserving transformations written in weakly recursive ILOG. We study a particular incarnation of this framework, the LILO algorithm, and show that it provides significant performance improvements over Edge ++ and that the constraints it introduces are efficiently enforced in practice. 1

Static Program Analyzers (SPA) are interactive tools that enhance program understanding during maintenance by answering queries about programs. Depending on the maintenance task in hand, SPAs must process different source programs and answer different types of program queries. Flexibility is, therefore, a desirable property of SPAs. In this paper, we describe a program query language, called PQL, that facilitates the design of flexible SPAs. PQL is a conceptual level, source language-independent notation to specify program queries and program views. In PQL, we can query global program design as well as search for detail code patterns. PQL queries are answered automatically by a query evaluation mechanism built into an SPA. Program design models and PQL form the core of an SPA conceptual model. We based the SPA's architecture on this conceptual model. By separating the conceptual model from the implementation decisions, we can design SPAs that are customizable to the needs of the mainte...

We investigate the optimization and evaluation of queries with universal quantification in the context of the object-oriented and object-relational data models. The queries are classified into 16 categories depending on the variables referenced in the so-called range and quantifier predicates. For the three most important classes we enumerate the known query evaluation plans and devise some new ones. These alternative plans are primarily based on anti-semijoin, division, generalized grouping with count aggregation, and set difference. In order to evaluate the quality of the many different evaluation plans a thorough performance analysis on some sample database configurations was carried out. The quantitative analysis reveals that---if applicable---the anti-semijoin-based plans are superior to all the other alternatives, even if we employ the most sophisticated division algorithms. Furthermore, exploiting object-oriented features, anti-semijoin plans can be derived even when this is not...

To support global transactions in a multidatabase environment, we must coordinate the activities of multiple Database Management Systems, that were designed for independent, stand-alone operation. The autonomy and heterogeneity of these systems present a major impediment to the direct adaptation of transaction management mechanisms developed for distributed database systems. In this paper we address the problems in multidatabase recovery. We show that most solutions proposed to provide multidatabase recovery are either allow incorrect results or place severe restrictions on global and local transactions. To assure that multidatabase recovery preserves the consistency of a multidatabase system, we introduce a multidatabase recoverability requirement. We also describe a recovery mechanism that takes advantage of the local recovery in the participating database systems by minimizing the replication of recovery tasks. 1 Introduction A Multidatabase System (MDBS) [15] is a facility that ...