Georges Gardarin

Evaluation of database recursive logic programs as recurrent function series

The authors introduce a new method to compile queries referencing recursively defined predicates. This method is based on an interpretation of the query and the relations as functions which map one column of a relation to another column. It is shown that a large class of queries with associated recursive rules, including mutually recursive rules, can be computed as the limit of a series of functions. Typical cases of series of functions are given and solved. The solutions lend themselves towards either extended relational algebra or SQL optimized programs to compute the recursive query answers. Examples of applications are given.

An implementation model for reasoning with complex objects

In this paper, we first propose a natural syntactical extension of DATALOG called NESTED_DATALOG for dealing with complex objects represented as nested predicates. Then, we introduce the token object model which is a simple extension of the relational model with tokens to represent complex objects and support referential information sharing. An implementation model of a NESTED_DATALOG program is defined by mapping it to the token object model which remains a straightforward extension of classical logical databases. Through this work, we can accommodate two basic requirements. The availability of a rule language for reasoning with complex objects, and the mechanism for mapping a complex object rule program to a relational DBMS offering a pure DATALOG rule language. In summary, the main contributions of the paper are the definition of a rule language for complex objects and the development of a technique to compile this complex object rule language to classical DATALOG.

A rule-based query rewriter in an extensible DBMS

An integrated approach to query rewriting in an extensible database server supporting ADTs, objects, deductive capabilities and integrity constraints is described. The approach is extensible through a uniform high level rule language used by the database implementor to specify optimization techniques. This rule language is compiled to enrich the strategy component and the knowledge base of the rewriter. Rules can be added to specify various aspects of query rewriting, including operation permutation, recursive query processing, integrity constraint addition, predicate simplification and method call simplification.<<ETX>>

OFL: a functional execution model for object query languages

We present a functional paradigm for querying efficiently abstract collections of complex objects. Abstract collections are used to model class extents, multivalued attributes as well as indexes or hashing tables. Our paradigm includes a functional language called OFL (Object Functional Language) and a supporting execution model based on graph traversals. OFL is able to support any complex object algebra with recursion as macros. It is an appropriate target language for OQL-like query compilers. The execution model provides various strategies including set-oriented and pipelined traversals. OFL has been implemented on top of an object manager. Measures of a typical query extracted from a geographical benchmark show the value of hybrid strategies integrating pipelined and set-oriented evaluations. They also show the potential of function result memorization, a typical optimization approach known as Memoization 2 in functional languages.

ESQL: An Extended SQL with Object and Deductive Capabilities

ESQL is an SQL upward-compatible database language that integrates in a uniform and clean way the essential concepts of relational, object-oriented and deductive databases. ESQL is intended for traditional data processing applications as well as more complex applications such as large expert systems. Therefore, ESQL’s salient features are: a rich and extendible type system based on abstract data types (ADTs) implemented in various programming languages; complex objects with object sharing by combining generic ADTs and object identity; the capability of querying and updating relations containing simple or complex objects using SQL-compatible syntax and semantics; and a DATALOG-like deductive capability provided as an extension of the SQL view mechanism.

Flora: A Functional-Style Language for Object and relational Algebra

Flora is a low-level language for implementing object-oriented databases. It is not intended as a user language, but rather as an intermediate language capable of supporting a variety of higher-level languages and applications. Flora has a very general data model with complex values and objects, constructs for specifying data storage, and a functionalstyle action language that incorporates set processing operations and a user-defined function capability. Flora provides the low-level building blocks that allow the calling language to appropriately model higher-level constructs such as classes and inheritance, and to build complex queries in a manner that readily supports various optimization schemes.

Translation of logic programs into functional fixpoint equations

Several methods to compile recursive function free Horn clause programs, called DATALOG, have been proposed in the literature. Most of them perform a rewriting of the rules using MAGIC or PROBLEM predicates in order to push selections before recursion. Rewritten rule systems are generally complex and difficult to translate in optimized relational algebra programs. Moreover, they generally generate too many results; thus, the query must be applied to the generated results to eliminate nonrelevant answers. After a survey of the existing compilation techniques which point out their limitations, we develop the magic function method. It is based on an interpretation of the query as a function which maps one column of a relation to another column. The rules are first translated into a connection graph and then, by a traversal of the associated graph, rewritten into a fixpoint functional equation. The resolution of this fixpoint equation using Tarskis theorem leads to efficient computations of the query answer. In particular, the derived algorithms push selections through recursion, because selections appear as function arguments. They generate only relevant answers to a given query. The purpose of this paper is mainly the introduction of a generalized method to obtain the fixpoint functional equation. The method is general enough to handle all binary rules, cyclic rules and function symbols. The main advantages of the method are: (1) It generates directly an optimized relational algebra program. (2) It performs a symbolic pre-computation which permits rule redundancy elimination. (3) It fully supports function symbols and range queries. Finally, an efficient execution algorithm working both on symbolic magic functions and data is proposed to evaluate recursive queries.

Design and Implementation of SABRE a Deductive and Parallel Database Machine

This paper reports on the design and architecture of the SABRE parallel database machine. It also presents a first design of the rule management functions which are currently being added to SABRE; with such an enhancement, the system will be a fully deductive MIMD knowledge machine offering among others a conversational knowledge manipulation language based on production rules and QUEL or SQL like queries. The main advantages of the system will be the power of the language to express problems, the generality of the approach and the efficiency of the machine.

Optimizing Path Expressions Using Navigational Algebraic Operators

Object-oriented database systems are more and more used in real applications due to their rich data model and query language mixing declarative assertions and navigations. Queries may frequently involve multiple collection traversais (i.e., path expression). Moreover, quantifiers like exist, any, all can also be included inside path expressions. These bring new challenges for object query optimization. In order to efficiently optimize these queries, we define the concept of annotated path expression and introduce two navigational algebraic operators, which mix nicely with classical object algebra. We introduce advanced query optimization techniques using the proposed extended algebra including a general framework and new rewriting rules for integrating navigational operators and traditional set-oriented operators. We also compare different navigation strategies for evaluating path expressions.

Integrating Classes and Relations to Model and Query Geographical Databases

Geographical databases require rich data models to represent geographical entities, relationships between these entities and geometric data. Furthermore, interactive spatial query languages should allow users to pose ad hoc queries in languages close to standards with high level graphical interfaces. This paper shows that a system mixing object-oriented and relational modelling capabilities with an extended SQL to query classes and relations is appropriate for modelling geographical data and interacting between a user and a GIS. Following these lines, a system is currently being implemented on top of an object server as an outcome of the IMPRESS ESPRIT project.