Much of relational algebra and the underlying principles of relational database design have a simple representation in the theory of domains that is traditionally used in the denotational semantics of programming languages. By investigating the possible orderings on powerdomains that are well-known in the study of nondeterminism and concurrency it is possible to show that many of the ideas in relational databases apply to structures that are much more general than relations. This also suggests a method of representing database objects as typed objects in programming languages. In this paper we show how operations such as natural join and projection -- which are fundamental to relational database design -- can be generalized, and we use this generalized framework to give characterizations of several relational database concepts including functional dependencies and universal relations. All of these have a simple-minded semantics in terms of the underlying domains, which can be thought ...

When a query fails, it is more cooperative to identify the cause of failure, rather than just to report the empty answer set. If there is not a cause for the query's failure, it is worthwhile to report the part of the query which failed. To identify a minimal failing subquery (MFS) of the query is the best way to do this. (This MFS is not unique; there may be many of them.) Likewise, to identify a maximal succeeding subquery (MSS) can help a user to recast a new query that leads to a non-empty answer set. Database systems do not provide the functionality of these types of cooperative responses. This may be, in part, because algorithmic approaches to finding the MFSs and the MSSs to a failing query are not obvious. The search space of subqueries is large. Despite work on MFSs in the past, the algorithmic complexity of these identification problems had remained uncharted. This paper shows the complexity profile of MFS and MSS identification. It is shown that there exists a simple algorit...

The problem of updating databases through interfaces based on the weak instance model is studied, thus extending previous proposals that considered them only from the query point of view. Insertions and deletions of tuples are considered. As a preliminary tool, a lattice on states is defined, based on the information content of the various states. Potential results of an insertion are states that contain at least the information in the original state and that in the new tuple. Sometimes there is no potential result, and in the other cases there may be many of them. We argue that the insertion is deterministic if the state that contains the information common to all the potential results (the greatest lower bound, in the lattice framework) is a potential result itself. Effective characterizations for the various cases exist. A symmetric approach is followed for deletions, with fewer cases, since there are always potential results; determinism is characterized consequently. 1 Introdu...

In many domains there are specific attributes in documents that carry more weight than the general words in the document. This paper proposes the use of information extraction techniques in order to identify these attributes for the domain of calls for papers. The utilisation of attributes into queries imposes new requirements on the retrieval method of conventional information retrieval systems. A new model for estimating the relevance of documents to user requests is also presented. The effectiveness of this model and the benefits of integrating information extraction with information retrieval are shown by comparing our system with a typical information retrieval system. The results show a precision increase of between 45% and 60% of all recall points. 1 Introduction Information retrieval (IR) systems, also called text retrieval systems, facilitate users to retrieve information which is relevant or close to their information needs. Even though specific words may be key attr...

this paper we propose to alleviate the usability problem by providing logical data independence to the nested relational model. To this end we extend the (classical) UR model to nested relations by defining the nested universal relation model (nested UR model). In particular, we extend the weak instance approach to the UR model to the nested weak instance approach to the nested UR model. EXAMPLE 1.1. Schemas of nested relations are represented graphically by scheme trees [17], such as T shown in Fig. 1.1. The nested relation scheme (NRS) of T, denoted by R(T), is: 6 AIRLINE AIR_CODE (FLIGHT_NO (PASSENGER)* (CREW)*)* (AIRPORT PORT_CODE)*, where the higher order attributes are marked with * in order to distinguish them from the zero order attributes [1]. ################## ################## ################## # # # # ################## # # # # ################# ################# ############################### ############################### # # # # ############################### # # # # ############################### # # # # AIR_CODE AIRLINE CREW PASSENGER FLIGHT_NO AIRPORT PORT_CODE FIG. 1.1. The scheme tree T. A null extended nested relation (abbreviated to nested relation), r*, over the NRS, R(T), for the scheme tree, T, of Fig. 1.1, is shown in Fig. 1.2. We note that null denotes a generic null value, whose semantics are represented by the partial ordering, null is less informative than any non-null value [17]. The semantics of r* can be expressed by a set of null functional dependencies (NFDs) and a set of null extended functional dependencies (NEFDs), both of which are members of the class of null extended data dependencies [17]. The NFDs that are satisfied in r* are: AIRLINE AIR_CODE, AIR_CODE AIRLINE, AIRPORT PORT_CODE and PORT_CODE AIRPORT. That is,...

Abstract. We present XyView, a practical solution for fast development of user- (web forms) and machine-oriented applications (web services) over a repository of heterogeneous schema-free XML documents. XyView provides the means to view such a repository as an array, queried using a QBE-like interface or through simple selection/projection queries. Close to the concept of universal relation, it extends it in mainly two ways: (i) the input is not a relational schema but a potentially large set of XML data guides; (ii) the view is not defined explicitly by a query but implicitly by various mappings so as to avoid data loss and duplicates generated by joins. Developed on top of the Xyleme content management system, XyView can easily be adapted to any system supporting XQuery. 1