Cluet, S., Delobel, C., "A General Framework for the Optimization of Object-Oriented Queries", Proceedings of the 1992.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....superfluous computations. Even more importantly, without additional optimizations this process ignores intra and inter data source integrity constraints . It has been recognized for some time that exploiting integrity constraints (so called semantic optimization) plays a crucial role in oodbs [CD92] and in integrating heterogenous data sources [QR95,LSK95] Relational database theory has studied extensively such issues [Mai83,Ull89,AHV95] but in the recent literature the use of constraints in optimization has been limited to special cases (see the related work in section 7) In contrast, we ....

.... constraints as equivalences between boolean valued (OQL actually) queries already appears in [FRV96] The equational theory of CoDi proves almost the entire variety of proposed algebraic query equivalences beginning with the standard relational algebraic ones, and including [SZ89a,SZ89b] [CD92,Clu91,FM95b,FM95a] and the very comprehensive work by Beeri and Kornatzky [BK93] Moreover, using especially (commute) CoDi validates and generalizes standard join reordering techniques, thus the problem of join associativity in object algebras raised in [CD92] does not arise. Our PC queries are less general than ....

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Sophie Cluet and Claude Delobel. A general framework for the optimization of object oriented queries. In M. Stonebraker, editor, Proceedings ACMSIGMOD International Conference on Management of Data, pages 383-- 392, San Diego, California, June 1992. Lucian Popa, Val Tannen

....and join elimination with referential integrity constraints are used. Surprisingly, very few experimental results are actually reported in these papers. 6] reports on join elimination in star queries that are less complex than our experiments with EC2. Examples of SQO for OO systems appear in [8, 2, 10, 13, 7]. A general framework for SQO using rewrite rules expressed using OQL appears in [12, 11] Techniques for using materialized views in query optimization are discussed in [5, 11, 12, 20, 3] A survey of the area appears in [16] From our perspective, the work on join indexes [21] and precomputed ....

Sophie Cluet and Claude Delobel. A general framework for the optimization of object oriented queries. In M. Stonebraker, editor, Proceedings ACM-SIGMOD pages 383-392, San Diego, California, June 1992.

....model of optimization is one that uses semantic knowledge about the logical schema: key constraints, functional dependencies, inclusion constraints such as foreign key constraints, inverse relationship constraints in OO schemas, etc. Semantic optimization [CGK 99, GGMR97, LS95, CGM90, FRV96, CD92] means finding rewritings, on the same logical schema, that are equivalent under the existing constraints with the original query. Typical transformations include join elimination, join introduction, predicate elimination or predicate introduction. These rewritings are, as in the previous case, ....

....each for index introduction and join elimination, both with queries and schemas of lesser complexity than what we have considered. CGK 99] reports on join elimination in star queries that are still less complex than our experiments with EC2. Examples of SQO for OO systems appear in [SZ89a, CD92, Clu91, BK93, FM95b, FM95a, GGMR97, CZ98] Use of referential integrity constraints to eliminate dependent joins is implicit in [JWKL90, CD92, KM90a, KM90b] A general framework for SQO using rewrite rules expressed 186 using OQL appears in [FRV96, Flo96] Techniques for using materialized ....

[Article contains additional citation context not shown here]

Sophie Cluet and Claude Delobel. A general framework for the optimization of object oriented queries. In M. Stonebraker, editor, Proceedings ACM-SIGMOD International Conference on Management of Data, pages 383--392, San Diego, California, June 1992.

.... optimization is quite comprehensive as it is possible to represent almost the entire variety of equivalences stated in various papers, beginning with the standard relational algebraic optimizations, continuing with OODB optimizations as in the work of Cluet, Zdonik, Maier, Fegaras and others [42, 43, 19, 18], and in fact including the very comprehensive work by Beeri and Kornatzky [8] Use of referential integrity constraints to eliminate dependent joins is implicit in Orion optimizations [26] and the type based approach of [19] This, and the use of precomputed ASR s appear in [28, 29] Precomputed ....

.... as in the work of Cluet, Zdonik, Maier, Fegaras and others [42, 43, 19, 18] and in fact including the very comprehensive work by Beeri and Kornatzky [8] Use of referential integrity constraints to eliminate dependent joins is implicit in Orion optimizations [26] and the type based approach of [19]. This, and the use of precomputed ASR s appear in [28, 29] Precomputed join indexes are proposed in [46] An approach to semantic query optimization using a translation into Datalog appears in [13, 24] The idea of using semantic constraints as rewrite rules is introduced and exploited ....

Sophie Cluet and Claude Delobel. A general framework for the optimization of object oriented queries. In M. Stonebraker, editor, Proceedings ACM-SIGMOD International Conference on Management of Data, pages 383--392, San Diego, California, June 1992.

....the result of a projection can be a set of record values (tuples) Since, however, algebraic optimization is crucial also for object databases, a dimensional object algebra will be defined. This algebra is obtained as a dimensional extension of object algebras that are the formalisms under OQL [6]. Classical algebraic identities will be revisited, to obtain a set of identities still holding between dimensional object algebra expressions, and to clarify how the new constructs dealing with data dimensionality interact with existing ones [11] ....

S. Cluet and C. Delobel. A General Framework for the Optimization of Object-Oriented Queries. In Proc. of the ACM SIGMOD Int'l Conf. on Management of Data, pages 383--392, 1992.

....is better suited for our translations than other proposals. Unlike other proposals, XML OQL was designed to have clear semantics in the form of a well de ned compositional translation into standard OQL (which in turn has clear formal semantics in the form of complex object algebras and calculi [10, 7]) It also supports a decidable typechecking system, well integrated with the type checking system of OQL. The semantics and type checking rules for XML OQL are given elsewhere [9] XML OQL is essentially OQL extended with XML path expressions and XML data constructions. For example, the ....

S. Cluet and C. Delobel. A General Framework for the Optimization of Object-Oriented Queries. In Proceedings of the ACM-SIGMOD International Conference on Management of Data, San Diego, California, pages 383-392, June 1992.

....maintenance plans (IMPs) at the algebraic level and, to the best of our knowledge, for object databases, is the rst one to do so. This makes it easier to integrate our solution into the kind of query processing frameworks that mainstream database management systems (DBMSs) rely on (e.g. [5]) When an MV is de ned, its de nition is traversed to identify the kinds of update events that might require propagation of changes to the MV. For each kind of event, an algebraic IMP is constructed that can compute the required changes 3 to the MV. The core of our solution is, therefore, the ....

S. Cluet and C. Delobel. A General Framework for the Optimization of ObjectOriented Queries. In Proc. SIGMOD, pages 383-392, 1992.

.... models [14] In fact, there are already several algebras for semi structured data, including an algebra based on structural recursion [4] YATL [12, 10] SAL [3] and x algebra [19] On the other hand, much research e ort has already been devoted to query algebras for complex data types [16, 11, 24], which have been used successfully as a formal basis for various optimization techniques for object oriented and object relational databases, such as path indexing [23] and query decorellation [13] However, very few of these algebras can handle tree data structures, such as those implicit to ....

....XML query language in the form of compositional transformation rules. Instead of inventing yet another algebra or calculus for expressing our semantic transformations, the target of our transformations is OQL, which, not only has precise semantics in the form of object algebras and calculi [16, 11], but has also been the focus of various optimization techniques, such as path indexing, path materialization, and query decorellation. These optimizations can now be used to speed up XML queries. Schema information is an indispensable component of our transformations. It is not only used to ....

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S. Cluet and C. Delobel. A General Framework for the Optimization of Object-Oriented Queries. In Proceedings of the ACM-SIGMOD International Conference on Management of Data, San Diego, California, pages 383-392, June 1992.

....to perform complementary semantic query optimizations in deductive objectoriented databases. 1 Introduction In object oriented database management systems, query optimization is performed by transforming algebraic expressions and by taking into account the physical representation of data [19][8]. Semantic query optimization takes advantage of the semantic knowledge (e.g. integrity constraints) about the content of databases to reformulate a query into a less expensive yet equivalent query. A number of techniques have been followed to perform semantic query optimization in classical ....

S. Cluet and C. Delobel. A general framework for the optimization of objectoriented queries. In Proc. of the ACM SIGMOD Int. Conf. on Management of Data, pages 383--392, San Diego, California, USA, June 1992.

....(U=S1(U) L= V=S1(V) U=S1(U) L=L,V=S1(V) U U U P P s s E(U,L,C) E(C,N,F) E(U,L,V) E(U,L,V) c U=root, L= country P g7(C) f7(db) h7(C) P (C) s s P (U=R1(root) l= V=R2(C) e s E(U,L,C) u=root, l= country Fig. 15 A query plan for bulk evaluation. databases [BCD89,CD92] and of semistructured data [FLMS99] The only restriction comes when the original query has the boolean predicate isempty: this introduces some transitive closure operators in the query plan, where optimizations are harder. However, most practical applications require only the positive fragment ....

Sophie Cluet and Claude Delobel. A general framework for the optimization of object oriented queries. In M. Stonebraker, editor, Proceedings ACM-SIGMOD International Conference on Management of Data, pages 383--392, San Diego, California, June 1992.

....the satisfiability problem for uniquetyped conjunctive queries is solvable in polynomial time. Most work on query optimization for an OODB implicitly assumes either a query language for complex objects with object identifiers or the type of an attribute is unique in the inheritance 5 hierarchy [17, 32, 33, 34, 7, 20, 27, 12]. Our work assumes an inheritance hierarchy in which type of an attribute need not be unqiue and hence our query model is more realistic than most previous work. We study the satisfiability problem by using typing contraints imposed by the inheritance hierarchy and the condition specified in a ....

Cluet, S. and Delobel, C., "A General Framework for the Optimization of Object-oriented Queries," Proceedings of the ACM SIGMOD , San Diego, CA, 1992, pp. 383-392.

....incomplete execution due to a SHORE server crash. From the measurements above it is clear that query unnesting o ers a signi cant performance improvement for the selected queries. 10. RELATED WORK There are many proposals for object query algebras [Leung et al. 1993; Danforth and Valduriez 1992; Cluet and Delobel 1992; Beeri and Kornatzky 1990; Pistor and Traunmueller 1986] In contrast to our algebra, these algebras support multiple bulk operators. But, as we have demonstrated in this paper, we get enough expressive power with just one operator, namely the monoid homomorphism. Supporting a small number of ....

....without using outer joins and grouping. There is an increasing number of recent proposals on OODB query optimization. Some of them are focused on handling nested collections [Ozsoyoglu and Wang 1992; Colby 1989] others on converting path expressions into joins [Kemper and Moerkotte 1990; Cluet and Delobel 1992], others on unnesting nested queries [Cluet and Moerkotte 1995b; Cluet and Moerkotte 1995a] while others are focused on handling encapsulation and methods [Daniels et al. 1991] Query decorrelation was rst introduced in the context of relational queries [Kim 1982; Ganski and Wong 1987; ....

Cluet, S. and Delobel, C. 1992. A General Framework for the Optimization of ObjectOriented Queries. In Proceedings of the ACM-SIGMOD International Conference on Management of Data, San Diego, California (June 1992), pp. 383-392.

....or a directed acyclic graph. Often, a subset relationship is tied to the subclass relationship. Queries in object bases may be evaluated on a single class, i.e. the set of the direct members of the class, or on a class including all its subclasses. Moreover, many query languages (e.g. O 2 SQL [3] or GOMql [5] allow queries to be formulated on arbitrary sets. As shown in [7, 8, 9] the access to the members of several classes by a common key attribute may be supported by a multiple set index structure for these classes. In the context of object bases two index structures based on the B ....

S. Cluet and C. Delobel. A general framework for the optimization of object-oriented queries. In Proc. of SIGMOD 1992, pages 383--392.

....of the outer queries cannot be promoted into the inner queries) The program that produced the performance results reported here is available at http: www cse.uta.edu fegaras unnest . 10 Related Work There are many proposals for object query algebras (see for example [LMS 93, DV92, CD92, BK90, PT86] In contrast to our algebra, these algebras support multiple bulk operators. But, as we have demonstrated in this paper, we get enough expressive power with just one operator, namely the monoid homomorphism. Supporting a small number of operators is highly desirable, since the more ....

....or the comprehension head) which cannot be unnested without using outer joins and grouping. There is an increasing number of recent proposals on OODB query optimization. Some of them are focused on handling nested collections [OW92, Col89] others on converting path expressions into joins [KM90, CD92] others on unnesting nested queries [CM95b, CM95a] while others are focused on handling encapsulation and methods [DGK 91] Query decorrelation was rst introduced in the context of relational queries [Kim82, GW87, Mur92] mostly in the form of source to source transformations. There is a ....

S. Cluet and C. Delobel. A General Framework for the Optimization of Object-Oriented Queries. Proceedings of the ACM-SIGMOD International Conference on Management of Data, San Diego, California, pages 383-392, June 1992.

....complemented by the algebraic optimization stage. ffl Where DBMS source code is available, the integrated architecture could benefit from an existing optmizer evaluator implementation for OQL. The object algebra underlying the DOQL translation approach is based on the algebras presented in [2, 8, 11]. The bulk operators of the algebra reflect the extent oriented nature of access to ODMG databases and also have a straightforward representation in terms of the algebraic interfaces supported by query optimization tools. The following bulk operators are supported: join(A,B,pred,outer) the join ....

S. Cluet and C. Delobel. A general framework for the optimization of object-oriented queries. In Proc. of the ACM SIGMOD Intl. Conference on Management of Data, pages 383--392, 1992.

....joins which have been the focus of our work. Also, we will concentrate on the execution of functional joins and ignore query optimization issues. Query optimization techniques which aim at finding the best evaluation order for chains of functional joins are presented in, e.g. GGT96] and [CD92] 1.3 Overview of this paper The remainder of this paper is organized as follows. In Sect. 2, we investigate alternative ways to implement object identifiers. Section 3 describes different algorithms for performing functional joins along single valued reference attributes. Section 4 describes ....

Cluet S, Delobel C (1992) A general framework for the optimization of object-oriented queries. In: Proc. of the ACM SIGMOD Conf. on Management of Data, June 1992, San Diego, Calif., pp 383--392

....of a long path in shorter binary paths. Efficient algorithms for traversing binary paths (i.e. join algorithms) are presented and compared in [Shekita90] A graph traversal approach [Jenq90] enables a long path to be traversed forward and backward. A variant approach is the typed algebra [Cluet92] which allows the Jenq et al. traversals to be described as binary algebra expressions. Another approach uses path indexes to directly achieve a whole navigation [Kemper90] A more general approach proposes using not only path indexes but also the physical information in linked objects to ....

....integrated into the language as common abstract collections. Indeed, conventional indexes can be seen as collections where an object or a set of objects is related to an atomic value [Kemper90] In object oriented databases, path indexes can be seen as collections providing a direct backward link [Cluet92]; or collections supporting reference chains from one object instance to another or to a collection of instances objects [Kemper90] in a way similar to multivalued attributes Cost Controlled OFL Rewriting Rules for Multiple Collection Traversals 4 Laboratoire PRiSM in user collections. Thus, ....

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Cluet S., Delobel C., "A General Framework for the Optimization of Object-Oriented Queries", intl. ACM SIGMOD Conf. on Management of Data, 1992.

....on some important issues identified by KARLAPALEM et al. 12] This section presents this set of heuristics that are implemented in our analysis algorithm for the fragmentation process that will be described next. 2. 1 Attributes, Methods and Relationships Complex attributes, complex methods [8] and relationships (generalization and composition) in the object oriented model define links between classes. These links generate navigational paths that must be considered in the fragmentation phase of the distribution design, in order to improve navigational query processing performance by ....

....define links between classes. These links generate navigational paths that must be considered in the fragmentation phase of the distribution design, in order to improve navigational query processing performance by reducing data transfer among sites. Also, different object clustering possibilities [7,8] transforms the analysis of those links into an essential task. Attribute links are easily identified by searching the database schema for attributes which domain is another class (such as an attribute 99 9999 9999 in class ) The method links ....

CLUET, S., DELOBEL, C., 1992, "A General Framework for the Optimization of Object-Oriented Queries". In: Proceedings of the 1992 ACM SIGMOD, vol. 21, n 2, San Diego, California, pp. 383-391

....paths that must be considered in the fragmentation phase of the distributed design, in order to improve navigational query processing performance by reducing data transfer among sites. Also, different object clustering possibilities transforms the analysis of those links into an essential task [14,15]. In order to propose heuristics for the distributed design of OODBs considering class attributes, methods and relationships, we present the following classification for classes in a database schema. This taxonomy is an extension of the existence dependency taxonomy presented in [1] and ....

Cluet, S., Delobel, C., "A General Framework for the Optimization of Object-Oriented Queries". In: Proc. of 1992 ACM SIGMOD, 21(2), pp. 383-391, San Diego, 1992

....one experiment each for index introduction and join elimination, both with queries and schemas of lesser complexity than what we have considered. 7] reports on join elimination in star queries that are still less complex than our experiments with EC2. Examples of SQO for OO systems appear in [28, 10, 9, 3, 14, 13, 17, 8] Use of referential integrity constraints to eliminate dependent joins is implicit in [19, 10, 20, 21] A general framework for SQO using rewrite rules expressed using OQL appears in [16, 15] Techniques for using materialized views in query optimization are discussed in [33, 31, 6, 15, 16, 30, ....

....than what we have considered. 7] reports on join elimination in star queries that are still less complex than our experiments with EC2. Examples of SQO for OO systems appear in [28, 10, 9, 3, 14, 13, 17, 8] Use of referential integrity constraints to eliminate dependent joins is implicit in [19, 10, 20, 21]. A general framework for SQO using rewrite rules expressed using OQL appears in [16, 15] Techniques for using materialized views in query optimization are discussed in [33, 31, 6, 15, 16, 30, 12] A survey of the area appears in [22] From our perspective, the work on join indexes [32] and ....

Sophie Cluet and Claude Delobel. A general framework for the optimization of object oriented queries. In M. Stonebraker, editor, Proceedings ACM-SIGMOD International Conference on Management of Data, pages 383-392, San Diego, California, June 1992. 20

....joins which have been the focus of our work. Also, we will concentrate on the execution of functional joins and ignore query optimization issues. Query optimization techniques which aim at finding the best evaluation order for chains of functional joins are presented in, e.g. GGT96] and [CD92] 1.3 Overview of this Paper The remainder of this paper is organized as follows: In Section 2 we investigate alternative ways to implement object identifiers. Section 3 describes di#erent algorithms for performing functional joins along single valued reference attributes. Section 4 describes ....

S. Cluet and C. Delobel. A general framework for the optimization of object-oriented queries. In Proc. of the ACM SIGMOD Conf. on Management of Data, pages 383--392, San Diego, CA, USA, June 1992.

....and a broad range of storage structures implemented on top of existing object servers. Algebraic Rewriting. Many optimization systems for object oriented query languages transform a query into an expression of a logical (object) algebra (e.g. VODAK ( AF95] Open OODB ( BMG93] as well as [CD92] Equivalences are defined on expressions of the algebra. The optimizer makes use of these equivalences by transforming expressions to find other algebraic representations of the query. Rule based optimizers heuristically prescribe direction and application of these transformations. Cost based ....

....We integrate dependency based optimization together with factorization into our optimizer but will provide cost based approaches to select the best plan in addition to heuristics. Factorization of Common Subexpressions. The idea of factorization is to evaluate identical subqueries only once. In [CD92] the common subexpression factorization is considered in more detail. Some systems restrict algebraic rewriting so that subexpressions which have been already detected will not be rewritten twice. In our approach, this rewriting is possible due to the chosen representation of the common ....

S. Cluet and C. Delobel. A General Framework for the Optimization of Object-- Oriented Queries. In Proc. of the ACM SIGMOD Conference, pages 383--392, San Diego, CA, 1992.

....conditions, access nested structure, or produce nested results, an essential feature found in these languages is the nesting of queries, i.e. the embedding of a query into another query. The optimization of object oriented (oo) queries has been intensively studied using algebraic rewriting [4, 7, 23, 24, 25] or rewriting of path expressions [7, 13, 14] However, in spite of the importance of nested queries, we do not know of any research on their optimization. Nested queries in the oo context are usually translated into nested algebraic expressions which are evaluated through rather inefficient ....

....nested results, an essential feature found in these languages is the nesting of queries, i.e. the embedding of a query into another query. The optimization of object oriented (oo) queries has been intensively studied using algebraic rewriting [4, 7, 23, 24, 25] or rewriting of path expressions [7, 13, 14]. However, in spite of the importance of nested queries, we do not know of any research on their optimization. Nested queries in the oo context are usually translated into nested algebraic expressions which are evaluated through rather inefficient nested loops. To a lesser extent, relational ....

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S. Cluet and C. Delobel. A general framework for the optimization of object-oriented queries. In Proc. of the ACM SIGMOD Conf. on Management of Data, pages 383--392, 1992.

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Cluet, S., Delobel, C., "A General Framework for the Optimization of Object-Oriented Queries", Proceedings of the 1992.

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Cluet, S. and Delobel, C. A general framework for the optimization of object-oriented Queries, Proc. ACM SIGMOD, San Diego, June 1992, pp 383-392.

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