Structured documents (e.g., SGML) can benefit a lot from database support and more specifically from object-oriented database (OODB) management systems. This paper describes a natural mapping from SGML documents into OODB's and a formal extension of two OODB query languages (one SQL-like and the other calculus) in order to deal with SGML document retrieval. Although motivated by structured documents, the extensions of query languages that we present are general and useful for a variety of other OODB applications. A key element is the introduction of paths as first class citizens. The new features allow to query data (and to some extent schema) without exact knowledge of the schema in a simple and homogeneous fashion. 1 Introduction Structured documents are central to a wide class of applications such as software engineering, libraries, technical documentation, etc. They are often stored in file systems and document access tools are somewhat limited. We believe that (object-oriented) d...

The widespread use of the Web has originated several new data management problems, such as extracting data from Web pages and making databases accessible from Web browsers, and has renewed the interest in problems that had appeared before in other contexts, such as querying graphs, semistructured data and structured documents. Several systems and languages have been proposed for solving each of these Web-data management problems, but none of these systems addresses all the problems from a unified perspective. Many of these problems essentially amount to data restructuring: we have information represented according to certain structure and we want to construct another representation of (part of) it using a different structure. We present the WebOQL system, which supports a general class of data restructuring operations in the context of the Web. WebOQL synthesizes ideas from query languages for the Web, for semistructured data and for website restructuring. 1 Introduction The widespre...

A query algebra is presented that expresses searches on structured text. In addition to traditional full-text boolean queries that search a pre-defined collection of documents, the algebra permits queries that harness document structure. The algebra manipulates arbitrary intervals of text, which are recognized in the text from implicit or explicit markup. The algebra has seven operators, which combine intervals to yield new ones: containing , not containing , contained in, not contained in, one of , both of , followed by . The ultimate result of a query is the set of intervals that satisfy it. An implementation framework is given based on four primitive access functions. Each access function finds the solution to a query nearest to a given position in the database. Recursive definitions for the seven operators are given in terms of these access functions. Search time is at worst proportional to the time required to solve the elementary terms in the query. Inverted indices yield search ...

: The user's conceptual model of a database system for geometric data should be simple and precise: easy to learn and understand, with clearly defined semantics, expressive: allow to express with ease all desired query and data manipulation tasks, efficiently implementable. To achieve these goals we propose to extend relational database management systems by integrating geometry at all levels: At the conceptual level, relational algebra is extended to include geometric data types and operators. At the implementation level, the wealth of algorithms and data structures for geometric problems developed in the past decade in the field of Computational Geometry is exploited. - The paper starts from a view of relational algebra as a many-sorted algebra which allows to easily embed geometric data types and operators. A concrete algebra for two-dimensional applications is developed. It can be used as a highly expressive retrieval and data manipulation language for geometric as well as standard...

. The paper introduces a model of the Web as an infinite, semistructured set of objects. We reconsider the classical notions of genericity and computability of queries in this new context and relate them to styles of computation prevalent on the Web, based on browsing and searching. We revisit several well-known declarative query languages (first-order logic, Datalog, and Datalog with negation) and consider their computational characteristics in terms the notions introduced in this paper. In particular, we are interested in languages or fragments thereof which can be implemented by browsing, or by browsing and searching combined. Surprisingly, stratified and well-founded semantics for negation turn out to have basic shortcomings in this context, while inflationary semantics emerges as an appealing alternative. 1 Introduction The World Wide Web [BLCL + 94] is a tremendous source of information which can be viewed, in some sense, as a large database. However, the nature of the Web is ...

: We describe the architecture of a relational database system that is extensible by user-defined data types and operations, including relation operations. The central concept is to use languages based on many-sorted algebra to represent queries as well as query execution plans. This leads to a simple and clean extensible system architecture, eases the task of an application developer by providing a uniform framework, and also simplifies rule-based optimization. As a case study the extensions needed for a geometric database system are considered. 1. Introduction Much of the database research of recent years was aimed at providing a better support for non-standard applications such as office information systems, geographic information systems, CAD databases, etc. A common need of these applications is the representation and manipulation of more complex objects than those representable by a tuple of a relation in the traditional relational model, for example, an office form, a complete ...

We propose a data model and query language that integrates an explicit modeling and querying of graphs smoothly into a standard database environment. For standard applications, some key features of object-oriented modeling are offered such as object classes organized into a hierarchy, object identity, and attributes referencing objects. Querying can be done in a familiar style with a derive statement that can be used like a select... from... where. On the other hand, the model allows for an explicit representation of graphs by partitioning object classes into simple classes, link classes, and path classes whose objects can be viewed as nodes, edges, and explicitly stored paths of a graph (which is the whole database instance). For querying graphs, the derive statement has an extended meaning in that it allows one to refer to subgraphs of the database graph. A powerful rewrite operation is offered for the manipulation of heterogeneous sequences of objects which often occur as a result of accessing the database graph. Additionally there are special graph operations like determining a shortest path or a subgraph and the model is extensible by such operations. Besides being attractive for standard applications, the model permits a natural representation and sophisticated querying of networks, in particular of spatially embedded networks like highways, public transport, etc.

We propose a framework for the specification of extensible database systems. A particular goal is to implement a software component for parsing and rule-based optimization that can be used with widely varying data models and query languages as well as representation and query processing systems. The key idea is to use second-order signature (and algebra), a system of two coupled many-sorted signatures, where the top-level signature offers kinds and type constructors and the bottom-level signature provides polymorphic operations over the types defined as terms of the top level. Hence the top level can be used to define a data or representation model and the bottom level to describe a query algebra or a query processing algebra. We show the applicability of this framework by examples drawn from relational modeling and query processing.

Observing that networks are ubiquitous in applications for spatial databases, we define a new data model and query language that especially supports graph structures. This model integrates concepts of functional data modeling with order-sorted algebra. Besides object and data type hierar-chies graphs are available as an explicit modeling tool, and graph operations are part of the query lan-guage. Graphs have three classes of components, namely nodes, edges, and explicit paths. These are at the same time object types within the object type hierarchy and can be used like any other type. Explicit paths are useful because “real world ” objects often correspond to paths in a network. Further-more, a dynamic generalization concept is introduced to handle heterogeneous collections of objects in a query. In connection with spatial data types this leads to powerful modeling and querying capa-bilities for spatial databases, in particular for spatially embedded networks such as highways, rivers, public transport, and so forth. We use multi-level order-sorted algebra as a formal framework for the specification of our model. Roughly spoken, the first level algebra defines types and operations of the query language whereas the second level algebra defines kinds (collections of types) and type con-structors as functions between kinds and so provides the types that can be used at the first level.

Relational database systems and most objectoriented database systems provide support for queries. Usually these queries represent retrievals over sets or multisets. Many new applications for databases, such as multimedia systems and digital libraries, need support for queries on complex bulk types such as lists and trees. In this paper we describe an object-oriented query algebra for lists and trees. The operators in the algebra preserve the ordering between the elements of a list or tree, even when the result list or tree contains an arbitrary set of nodes from the original tree. We also present predicate languages for lists and trees which allow order-sensitive queries because they use pattern matching to examine groups of list or tree nodes rather than individual nodes. The ability to decompose predicate patterns enables optimizations that make use of indices.