We present the Lorel language, designed for querying semistructured data. Semistructured data is becoming more and more prevalent, e.g., in structured documents such as HTML and when performing simple integration of data from multiple sources. Traditional data models and query languages are inappropriate, since semistructured data often is irregular, some data is missing, similar concepts are represented using different types, heterogeneous sets are present, or object structure is not fully known. Lorel is a user-friendly language in the SQL/OQL style for querying such data effectively. For wide applicability, the simple object model underlying Lorel can be viewed as an extension of ODMG and the language as an extension of OQL. The main novelties of the Lorel language are: (i) extensive use of coercion to relieve the user from the strict typing of OQL, which is inappropriate for semistructured data

Lore (for Lightweight Object Repository) is a DBMS designed specifically for managing semistructured information. Implementing Lore has required rethinking all aspects of a DBMS, including storage management, indexing, query processing and optimization, and user interfaces. This paper provides an overview of these aspects of the Lore system, as well as other novel features such as dynamic structural summaries and seamless access to data from external sources.

We consider the problem of storing and accessing documents (SGML and HTML, in particular) using database technology. To specify the database image of documents, we use structuring schemas that consist in grammars annotated with database programs. To query documents, we introduce an extension of OQL, the ODMG standard query language for object databases. Our extension (named OQL-doc) allows to query documents without a precise knowledge of their structure using in particular generalized path expressions and pattern matching. This allows us to introduce in a declarative language (in the style of SQL or OQL), navigational and information retrieval styles of accessing data. Query processing in the context of documents and path expressions leads to challenging implementation issues. We extend an object algebra with new operators to deal with generalized path expressions. We then consider two essential complementary optimization techniques: 1. we show that almost standard database optim...

This paper presents dedale, a spatial database system intended to overcome some limitations of current systems by providing an abstract and non-specialized data model and query language for the representation and manipulation of spatial objects. dedale relies on a logical model based on linear constraints, which generalizes the constraint database model of [KKR90]. While in the classical constraint model, spatial data is always decomposed into its convex components, in dedale holes are allowed to fit the need of practical applications. The logical representation of spatial data although slightly more costly in memory, has the advantage of simplifying the algorithms. dedale relies on nested relations, in which all sorts of data (thematic, spatial, etc.) are stored in a uniform fashion. This new data model supports declarative query languages, which allow an intuitive and efficient manipulation of spatial objects. Their formal foundation constitutes a basis for practical query optimizati...

We present a class of path constraints of interest in connection with both structured and semistructured databases, and investigate their associated implication problems. These path constraints are capable of expressing natural integrity constraints that are not only a fundamental part of the semantics of the data, but are also important in query optimization. We show that in semistructured databases, despite the simple syntax of the constraints, their associated implication problem is r.e. complete and finite implication problem is co-r.e. complete. However, we establish the decidability of the implication problems for several fragments of the path constraint language, and demonstrate that these fragments suffice to express important semantic information such as inverse relationships and local database constraints commonly found in object-oriented databases. We also show that in the presence of types, the analysis of path constraint implication becomes more delicate. We demonst...

We study the problem of maintaining materialized views of graph structured data. The base data consists of records containing identifiers of other records. The data could represent traditional objects (with methods, attributes, and a class hierarchy), but it could also represent a lower level data structure. We define simple views and materialized views for such graph structured data, analyzing options for representing record identity and references in the view. We develop incremental maintenance algorithms for these views, and discuss how to realize these algorithms when only a data warehouse (and not the data sources) knows the view definition. 1 Introduction Relational views are useful for controlling data access, specifying contents of caches (or remote copies), and other data management tasks. In this paper we study how to extend this view concept and the associated maintenance algorithms to what we call a graph structured database (GSDB). Informally, a GSDB is a collection of "o...

Applications have an increasing need to manage semistructured data (such as data encoded in XML) along with conventional structured data. We extend the structured object database model ODMG and its query language OQL with the ability to handle semistructured data based on the OEM model and Lorel language, and we implement our extensions in a system called Ozone. In our approach, structured data may contain entry points to semistructured data, and vice-versa. The unified representation and querying of such "hybrid" data is the main contribution of our work. We retain strong typing and access to all properties of structured portions of the data while allowing flexible navigation of semistructured data without requiring full knowledge of structure. Ozone also enhances both ODMG/OQL and OEM/Lorel by virtue of their combination. For instance, Ozone allows OEM semantics to be applied to ODMG data, thus supporting semistructured-style navigation of structured data. Ozone als...

We propose a language for declarative specification of mappings between different object-oriented multidatabases. The language is based on OSQL, the query language of the IRIS OODBMS. We also outline the operational semantics of our language. To appear in Distributed Object Management, M. T. Ozsu, U. Dayal and P. Valduriez, editors, Morgan Kaufmann Publishers, 1993. y Work performed while visiting HP Labs, Palo Alto, California. Address: Department of Computing and Information Sciences, 234 Nichols Hall, Kansas State University, Manhattan, KS 66506-2302. Email: chomicki@cis.ksu.edu. z Work performed while visiting Santa Clara University and HP Labs, Palo Alto, California. Email: litwin@hplabs.hp.com. 1 Introduction Declarative definition of multidatabase mappings is one of the central problems of multidatabase interoperability. For object-oriented (OO) databases, one may need to map types (classes) in one database into types in another database, or functions into functions, or...

We argue that, despite a substantial number of proposed and existing new database systems, a suitable database system for software development environments and especially process-centred environments does not yet exist. We do so by reviewing and refining the requirements for such systems in detail based on a number of examples. We then sketch a number of available and archetypical database systems and indicate why they do not meet these requirements. 1 This report has been published in: I. Sommerville and M. Paul, editors, Software Engineering ESEC '93 --- Proc. of the 4 th European Software Engineering Conference, Garmisch Partenkirchen, Germany, volume 717 of Lecture Notes in Computer Science, pages 145--162, Springer 1993. 1 Introduction Software development environments (SDEs) include tools which support most of the software life-cycle phases, i.e. construction and analysis of the corresponding documents and document interdependencies. Sophisticated integrated environments en...

There are many applications where an object oriented data model is a good way of representing and querying data. However, current object database systems are unable to handle the case of objects whose attributes are uncertain. In this paper, extending previous pioneering work by Kornatzky and Shimony, we develop an extension of the relational algebra to the case of object bases with uncertainty. We propose concepts of consistency for such object bases, together with an NP-completeness result, and classes of probabilistic object bases for which consistency is polynomially checkable. In addition, as certain operations involve conjunctions and disjunctions of events, and as the probability of conjunctive and disjunctive events depends both on the probabilities of the primitive events involved as well as on what is known (if anything) about the relationship between the events, we show how all our algebraic operations may be performed under arbitrary probabilistic conjunction and ...