eeply, you will note that we generate query results solely through the side-e#ect free construction of values from simpler constituents and that functional composition will be the predominant way of forming complex queries. Referential transparency is the key to transformational programming and equational reasoning. Relatively few components are needed in our initial query language core. We grow this language through function definitions of the form f # e where e is an expression built from components we have already introduced. The functions f so defined will get more complex as we go on until we are ready to give the meaning of SQL, OQL [1.4], or XPath [1.1] query clauses such as select-from-where, exists-in, flatten, or path expressions. 1.1.1 Notation, Types, and Values If you are familiar with notational conventions of functional programming languages such as Haskell [1.14] you will feel at home right away. Figure 1.1 introduces the core expression forms e and their notation.

This paper describes a multi-agent platform to be used for the integration of environmental information that may be distributed over a network. The system is designed to work as a collection of collaborating agents. Information sources are encapsulated as data source agents that accept messages in an agent communication language. Here we describe how queries can be entered into the system and information collected from multiple sources. A key component of the query module is the planner agent, which takes a query and transforms it first to a calculus, then to an algebraic expression in order to break it into subqueries which an executor agent can send to the data source agents. As part of this process, the query is translated from user level ontologies to lower level ontologies relevant to the data source agents. Query results need not be returned within an ACL message, but may instead be represented by a CORBA object reference which may be used to obtain the result set. The architecture and operation of these agent components is described and an example is presented of how environmental information can be queried. 1

The stora: ar ara:S2 oflaI( aI nts oftime-va ryingspag2S aa aag2a da ta is becominga importao fear re of ma yaI licaI:2 domam2D Thisha fuelled the need forspaS:)) empora extensions to da2 modelsad their aeir2 aei queryingfaying2DD . Toda)I much of this workha focused on therela tiona dan model, with objectdae models receivingfa less consideransid Where descriptions of such object models do exist, these modelsfae to fully integrae theirspar2SI aar2a aa tempora dimensions intoa uniformaj coherent model. Ina2DjKOO2 there is currentlya laS of systems which build upon these models to producedae2ID eaI:DK ecturestha aares the broa spectrum of issuesrela ed to the delivery ofa fully functiona spai o-tempora DBMS. This pas2 presentsa founda2 on for the development of such a system,catem Tripod, by describinga spa tio-historica object modelbaSz ona speciazIID mechaI sm, ca,2z history, forma2I a2ID knowledge adge entitiestha cha ge over time. KeyfeazIKS of the resulting model include: (i) consistent representaK ons of primitive spaea aa timestam types; (ii)a component -baSS design in whichspa:((z timestam am historica extensionsan formarm2S incrementarem for subsequent use together orsepaK) ely; (iii) compa ibility with mah2 trea query processingfrazD orks for objectda taect2: a d (iv) the integ raeg2 of thespaDzSK empora prop with the ODMG object daect2 e staO:( d. Thepa per presentsa comprehensiveforma chaDOK)j2qI tion of the modela d illustrazK its cas2 ilities ina crimedam mame2I enta2DIKOj2qIS It isa2D shown how the model ca beprogra med usinga extension to the ODMGlaOjzj2 bindings. The modela dlazzO(2 bindingshad been fully implemented.

Modern database systems provide not only powerful data models but also complex query languages supporting powerful features such as the ability to create new database objects and invocation of arbitrary methods (possibly written in a third-party programming language).

I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. iii Client applications submit streams of relational queries to database servers. For simple requests, inter-process communication costs account for a significant portion of user-perceived latency. This trend increases with faster processors, larger memory sizes, and improved database execution algorithms, and this trend is not significantly offset by improvements in communication bandwidth. Caching and prefetching are well studied approaches to reducing user-perceived latency. Caching is useful in many applications, but it does not help if future requests rarely match previous requests. Prefetching can help in this situation, but only if we are able to predict future requests. This prediction is complicated in the case of relational queries by the presence of request parameters: a prefetching algorithm must predict not only a query that will be executed in the future,

This paper contributes a general approach to characterizing patterns of change in a spatio-temporal database. While there is a particular interest in modelling and querying how spatio-temporal entities evolve, the approach contributed by the paper is distinctive in being applicable without modification to aspatial entities as well. The paper uses the Tripod spatio-temporal model to describe and instantiate in detail the contributed approach. After briefly describing a typical application and providing basic knowledge about Tripod, the paper characterizes and classifies evolution queries and describes in detail how they are evaluated.

Abstract Spatio-temporal extensions to data models have been an active area of research for a number of years. To date, much of this work has focused on the relational data model, with object data models receiving far less consideration. This paper presents a spatio-historical object model that uses a specialized mechanism, called a history, to maintain knowledge about entities that change over time. Key features of the resulting proposal include: (i) consistent representations of primitive spatial and temporal types; (ii) a component-based design in which spatial, temporal and historical extensions are formalized incrementally, for subsequent use together or separately; (iii) a formally specified data model. The model can be used directly during the design of spatio-historical applications, but also forms the basis of an implementation activity developing a spatio-historical object database management system. 1

Pheasant is the first proposal for a declarative domain specific visual query language for HEP data analysis. It has been designed based on our experience dealing with HeraB event data and query patterns. Its main goal is to allow the physicist to describe the decay selection queries by means of visual operators, to be run against the experiments' existing storage bases and analysis frameworks.

In FIPA-style multi-agent systems, agents coordinate their activities by sending messages representing particular communicative acts (or performatives). Agent communication languages must strike a balance between simplicity and expressiveness by defining a limited set of communicative act types that fit the communication needs of a wide set of problems. More complex requirements for particular problems must then be handled by defining domain-specific predicates and actions within ontologies. This paper examines the communication needs of a multi-agent distributed information retrieval system and discusses how well these are met by the FIPA ACL.

Abstract. The research community is addressing a number of issues in response to an increased reliance of organisations on data warehousing. Most work addresses aspects related to the internal operation of a data warehouse server, such as selection of views to materialise, maintenance of aggregate views and performance of OLAP queries. Issues related to data warehouse maintenance, i.e. how changes to autonomous sources should be detected and propagated to a warehouse, have been addressed in a fragmented manner. We have shown earlier that a number of maintenance policies based on source characteristics and timing are relevant and meaningful to single source views. In this report we detail how this work has been extended for multiple sources. We focus on exploring policies for data integration from heterogeneous sources. As the number of policies is very large, we first analyse their behaviour intuitively with respect to broader source and policy characteristics. Further, we extend the single source cost model to these policies and incorporate it into a Policy Analyser for Multiple sources (PAM). We use this to analyse the effect of source characteristics and join alternatives on various policies. We have developed a Testbed for Maintenance of Integrated Data (TMID). We report on experiments conducted to validate the policies that are recommended by the tool, and confirm our initial analysis. Finally, we distil a set of heuristics for the selection of multi-source policies based on quality of service and other requirements. 1.