Sophie Cluet and Guido Moerkotte. Nested queries in object bases. In Proceedings of the Fourth International Workshop on Database Programming Languages - Object Models and Languages, pages 226-242, New York City, NY, USA, 1993.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....queries to concrete evaluation algorithms. We are presenting a new XML algebra and a query optimization framework based on query normalization and query unnesting (also known as query decorrelation) There are many proposals on query optimization that are focused on unnesting nested queries [23, 18, 26, 11, 12, 9, 28]. Nested queries appear more often in XML queries than in relational queries, because most XML query languages, including XQuery, allow complex expressions at any point in a query. Current commercial database systems typically evaluate nested queries in a nested loop fashion, which is unacceptable ....

S. Cluet and G. Moerkotte. Nested Queries in Object Bases. In Fifth International Workshop on Database Programming Languages, Gubbio, Italy, page 8, September 1995. 12

.... 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 schema less XML data. But if an XML schema is provided, then XML data can be easily mapped to complex data, while XML queries can be translated into algebraic forms in one of these complex data ....

S. Cluet and G. Moerkotte. Nested Queries in Object Bases. In Fifth International Workshop on Database Programming Languages, Gubbio, Italy, page 8, Sept. 1995.

.... expressions is left to PostgreSQL while the evaluation of RQL functions for traversing class and property hierarchies relies on the existence of appropriate indices (see the last paragraph) The main difficulty in translating an entire RQL algebraic expression (expressed in an object algebra a la [9]) to a single SQL3 query is due to the fact that most RQL path expressions interleave schema with data querying [8] This is the case of the query Q1 presented previously. The left part of figure 9 illustrates the algebraic translation of Q1. The translation of the nested query given in shadowbox ....

S. Cluet and G. Moerkotte. Nested Queries in Object Bases. In DBPL'93, pages 226--242, 1993. 21

....which integrates data from different sources such as object databases or semi structured web repositories. The authors have proposed only two new operators , namely the Bind and the Tree operators. All others are standard operators drawn from earlier work on Relational Algebra and Object Algebra[16]. Starting from an arbitrary XML structure, the Bind operation is applied, whose purpose is to extract the relevant information and produce a structure called Tab, which is comparable to a 1NF relation. Then, on the Tab structures, standard operators such as Join, Select, Project can be applied. ....

....operation providing support for type filtering and horizontal and vertical navigation. User queries are optimized by generating integration views locally or by pushing queries to the external source. The Tree operation is a sequence of Group, Sort and Map operations which are Object algebra [16] operators on which optimization techniques of Object algebra can be used. This XML algebra is better than the IBM Algebra since it is optimizable. The drawback is that the authors have developed it in the context of an integration system using their own data model and type system and not provided ....

S. Cluet and G. Moerkotte. Nested Queries in Object Bases. In Proceedings of International Workshop on Database Programming Languages, pages 226-242, New York City, USA, August 1993.

....database. Optimization Different optimization techniques can be applied to the view management system. Indexing can be automatically performed on root objects and core attributtes to speed up the evaluation of characteristic functions. Also, nested query optimization techniques for object bases [CM93] can be adapted to nested view definitions (which implicitly define nested queries) so as to obtain more efficient characteristic functions. Lazy materialization also plays an important role in making the view mechanism effective and should be largely exploited. 7 Conclusion In this paper, we ....

Sophie Cluet and Guido Moerkotte. Nested Queries in Object Bases. Technical report, FIDE 2 ESPRIT Project, 1993.

....and freeing up more time for an optimizer to perform its search. Still to write about: ffl Opt [KD] 7. 3 Transforming Nested Queries Still to write about: ffl Kim [Kim82] ffl Ganski Wong [GW87] ffl Dayal [Day87] ffl Magic Sets [MP92, SPL96, SHP 96b] ffl Cluet and Moerkotte [CM95, CM93] ffl Steenhagen [SABd94] 7.4 Semantic Optimization and Handling Foreign Functions ffl Zdonik [HZ80] ffl Aberer [AF95] ffl Chaudhuri and Kim [CS96, CS93] ffl Conjunctive Predicates [HS93, Hel94, LMS94] ffl Avoiding sorting [SSM96] ffl Semantics and Cost Estimation [NCN97] 7.5 Plan ....

Sophie Cluet and Guido Moerkotte. Nested queries in object bases. In Proc. 4th Int'l Workshop on Database Programming Languages, NY, NY, August 1993. SpringerVerlag.

....converts the null e s into empty sets. Q (d;e) d (X) is a generalized projection that retrieves the d component of each pair (d; e) in X and removes the duplicate d s. 7. QUERY UNNESTING There are many recent proposals on OODB query optimization that are focused on unnesting nested queries [Cluet and Moerkotte 1995a; Cluet and Moerkotte 1995b; Claussen et al. 1997; Steenhagen et al. 1994] also known as query decorrelation) Nested queries appear more often in OODB queries than in relational queries, because OODB query languages allow complex expressions at any point in a query. In addition, OODB types are ....

....empty sets. Q (d;e) d (X) is a generalized projection that retrieves the d component of each pair (d; e) in X and removes the duplicate d s. 7. QUERY UNNESTING There are many recent proposals on OODB query optimization that are focused on unnesting nested queries [Cluet and Moerkotte 1995a; Cluet and Moerkotte 1995b; Claussen et al. 1997; Steenhagen et al. 1994] also known as query decorrelation) Nested queries appear more often in OODB queries than in relational queries, because OODB query languages allow complex expressions at any point in a query. In addition, OODB types are allowed to have attributes ....

[Article contains additional citation context not shown here]

Cluet, S. and Moerkotte, G. 1995b. Nested Queries in Object Bases. In Fifth International Workshop on Database Programming Languages, Gubbio, Italy (Sept. 1995), pp. 8.

....converts the null e s into empty sets. Q (d;e) d (X) is a generalized projection that retrieves the d component of each pair (d; e) in X and removes the duplicate d s. 7 Query Unnesting There are many recent proposals on OODB query optimization that are focused on unnesting nested queries [CM95b, CM95a, CKMP97, SAB94] sometimes called query decorrelation) Nested queries appear more often in OODB queries than in relational queries, because OODB query languages allow complex expressions at any point in a query. In addition, OODB types are allowed to have attributes with collection values ....

....Since OODB queries are far more complex than relational queries, it is more crucial to express the unnesting transformations in a formal algebra that will allow us to prove the soundness and completeness of these transformations. The rst work with that goal in mind was by Cluet and Moerkotte [CM95b, CM95a] which covered many cases of nesting, including nested aggregate queries, and validated all the transformations. Their work was extended by Claussen et al. CKMP97] to include universal quanti cation. Cherniack and Zdonik [CZ98a, CZ98b] have used formal methods to validate query unnesting ....

[Article contains additional citation context not shown here]

S. Cluet and G. Moerkotte. Nested Queries in Object Bases. In Fifth International Workshop on Database Programming Languages, Gubbio, Italy, September 1995.

....the data model of the Lore system. Several query languages have been proposed for SSD [1, 2, 9] along with systems for storing, browsing and querying such data. Algebras for oo databases were extended to deal with features relevant to SSD; e.g. the algebra for handling nested queries presented in [6, 7] was extended in [4] to handle general path expressions (GPEs) 12] extended the traditional SPJ algebra into a navigational algebra for the Web, by adding two new operators (unnesting a nested list inside an HTML page, and following an HTML link) It also proposed a cost model for query ....

....query languages for XML. Like existing algebras, it can serve to provide a concise representation of query execution, that still leaves room for various decisions about actual execution plans, and supports rewritebased and cost based optimizations. It has been influenced by the work in [6, 7], with extensions that we believe are relevant to the XML format. The XML data format presents some challenges. Being a textual format, it has order built into it. A query language needs to allow the users to view the data as ordered. Although lists have been treated in languages for complex ....

S. Cluet and G. Moerkotte. Nested queries in object bases. Technical Report 95-6, RWTH-Aachen, 1995.

....the data model of the Lore system. Several query languages have been proposed for SSD [1, 2, 9] along with systems for storing, browsing and querying such data. Algebras for oo databases were extended to deal with features relevant to SSD; e.g. the algebra for handling nested queries presented in [6, 7] was extended in [4] to handle general path expressions (GPEs) 12] extended the traditional SPJ algebra into a navigational algebra for the Web, by adding two new operators (unnesting a nested list inside an HTML page, and following an HTML link) It also proposed a cost model for query ....

....query languages for XML. Like existing algebras, it can serve to provide a concise representation of query execution, that still leaves room for various decisions about actual execution plans, and supports rewritebased and cost based optimizations. It has been influenced by the work in [6, 7], with extensions that we believe are relevant to the XML format. The XML data format presents some challenges. Being a textual format, it has order built into it. A query language needs to allow the users to view the data as ordered. Although lists have been treated in languages for complex ....

[Article contains additional citation context not shown here]

S. Cluet and G. Moerkotte. Nested queries in object bases. In Proc. DBPL, 1993.

....mapped to map a 2 , a 1 document( A 1 a 1 , Paragraph ) # map a 2 , a 1 .section.document ( A 1 a 1 , Paragraph ) 8. In older object oriented algebras this was not always the case, see e.g. 25] On the other hand, our map operator is comparable to the operator denoted by # a:e in [10]. 13 2. Equivalent Conditions This type is very similar to the previous one, except that here we consider only the equivalence of boolean expressions: x IN C: cond 1 (x) # cond 2 (x) We can translate this kind of equivalence also into a transformation rule of the query algebra by lifting ....

....matching. In this paper we have excluded the issue of nested queries, which is of considerable interest for semantic query optimization based on equivalences as many equivalences give rise to rules involving nested queries. Some interesting transformation rules for nested queries can be found in [10]. A completely different approach to query optimization in the presence of methods can be found in the REVELATION Project [13] objects are asked to reveal the implementation of methods during query optimization. This differs from our approach as we are not interested in the implementation itself ....

S. Cluet, G. Moerkotte: "Nested Queries in Object Bases", Proc. DBPL4, Manhattan, New York City, August 30th --September 1st, 1993.

....plans. This framework is reminiscent of inherited and synthesized attributes for attribute grammars. There are many recent proposals on OODB query optimization. Some of them are focused on converting path expressions into joins [12, 5] while others are focused on unnesting nested queries [7, 6, 4]. Query nesting appears more often in OODB queries than in relational queries, since OODB queries permit complex expressions at any point of a query. Therefore, query unnesting is a crucial component of any OODB optimizer. Even though there is already a number of proposed techniques for query ....

S. Cluet and G. Moerkotte. Nested Queries in Object Bases. In Fifth International Workshop on Database Programming Languages, Gubbio, Italy, September 1995.

....into an NF 2 algebra has been presented in [RoKS88] however, little attention has been paid to efficiency. Work has been done on the implementation of the extended NF 2 query language HDBL of the AIM project [SLPW89, SuLi90] to our knowledge HDBL has not been translated into an algebra. In [ClMo93] a proposal for the optimization of nested O 2 SQL queries has been made. O 2 SQL is translated into an extension of the GOM algebra [KeMo93] and examples of optimization of nested algebra queries are given. The organization of this paper is as follows. In Section 2 nesting in the various ....

....with nesting in the where clause, however, techniques presented apply to nested queries with nesting in the select clause as well. Following the relational line of work, the goal in translation and optimization of OOSQL is to move from tuple to set oriented query processing. Our approach, as in [ClMo93] is to translate nested OOSQL queries into nested algebraic expressions, and then to try to rewrite nested algebraic expressions into join expressions. In the following section, we briefly present the algebraic language ADL. 3 The Complex Object Algebra ADL The language ADL is a typed algebra ....

Cluet, S. and G. Moerkotte, "Nested Queries in Object Bases," Proceedings Fourth International Workshop on Database Programming languages, New York, Sept. 1993.

....]x; unit[list ]y) j x E 1 ; y E 2 gg Such arbitrary value constructions lead to complex nesting or grouping expressions and inherent problems with common subexpression detection (note the multiple use of x and y in the constructor) in the variable less algebraic approaches. Recent efforts [CM93, Ste95] have enhanced algebras with special operators to cope with the important (but not all) cases. Unfortunately, these operators do enjoy few interesting algebraic properties making them hard to treat during rewrite optimization. 3.1 A Rewriting Example Now that we have an idea of how to ....

....(E 2 ) objects, which is exactly what is needed for the evaluation of queries with nesting in the select clause: E 1 Delta x;y:f(x) p(x;y) c(x;y) g E 2 = ff(x) Phi hg = fc(x; y) j y E 2 ; p(x; y)gi j x E 1 g See [SABdB94] for a detailed discussion of the nestjoin s characteristics. CM93] achieves functionality similar to the nestjoin by introducing a binary grouping operator. Now, revisiting the query rewriting above, we detect the characteristic pattern of a semijoin at ( By matching the semijoin s defining comprehension against the query we recognize a subquery that can be ....

Sophie Cluet and Guido Moerkotte. Nested Queries in Object Bases. In Proceedings of the 4th Int'l Workshop on Database Programming Languages (DBPL), September 1993.

....of the relational operator, project: it evaluates the expression h E=e.name, C=c. name i for every input element and constructs a set from these tuples using [ 7 Query Unnesting There are many recent proposals on OODB query optimization that are focused on unnesting nested queries [CM95b, CM95a, CKMP97, SAB94] Query nesting appears more often in OODB queries than in relational queries, because OODB query languages allow complex expressions at any point in a query. In addition, OODB types are allowed to have nested attributes, which lead naturally to nested queries. Current OODB ....

....Since OODB queries are far more complex than relational queries, it is more crucial to express the unnesting transformations in a formal algebra that will allow us to prove the soundness and completeness of these transformations. The first work with that goal in mind was by Cluet and Moerkotte [CM95b, CM95a] which covered many cases of nesting, including nested aggregate queries, and validated all the transformations. This section describes a query unnesting algorithm for a subset of the monoid comprehension calculus in which comprehensions over idempotent monoids (such as, and ) ....

[Article contains additional citation context not shown here]

S. Cluet and G. Moerkotte. Nested Queries in Object Bases. In Fifth International Workshop on Database Programming Languages, Gubbio, Italy, September 1995.

.... by using outer joins combined with grouping [13, 6] In most OODB algebras, where grouping is an explicitly supported operator and can appear in any place in an algebraic form, any form of query nesting can be unnested by promoting the inner queries one level up in the query nesting hierarchy [3, 4]. This results to a large flat join, which is the concatenation of all the joins from every level in the nested query. Furthermore, all unnesting methods proposed in the literature introduce additional operators, such as outer joins and grouping, thus increasing the number of operators to be ....

S. Cluet and G. Moerkotte. Nested Queries in Object Bases. In Fifth International Workshop on Database Programming Languages, Gubbio, Italy, September 1995.

....regarding the extent to which the store technology is tuned to the requirements of the particular language supported [Brown et al. 1992] and the extent to which the store builds in clustering, indexes, bulk types, etc. Cluet Delobel, 1991, Matthes Schmidt, 1991, Zezula Rabitti, 1992, Cluet Moerkotte, 1993]. Some persistent extensions to languages accept that they cannot implement all four of the tasks listed above. For example, the Texas store [Singhal et al. 1992] provides a stable checkpointable memory in which C and C programs run. In consequence it provides orthogonal persistence for those ....

Cluet, S. & Moerkotte, G., 1993. Nested Queries in Object Bases . ESPRIT BRA Project 6309 FIDE 2 Technical Report FIDE/93/69.

....database. Optimization Different optimization techniques can be applied to the view management system. Indexing can be automatically performed on root objects and core attributtes to speed up the evaluation of characteristic functions. Also, nested query optimization techniques for object bases [CM93] can be adapted to nested view definitions (which implicitly define nested queries) so as to obtain more efficient characteristic functions. Lazy materialization also plays an important role in making the view mechanism effective and should be largely exploited. 7 Conclusion In this paper, we ....

Sophie Cluet and Guido Moerkotte. Nested Queries in Object Bases. Technical report, FIDE 2 ESPRIT Project, 1993.

.... avoided by using outer joins combined with grouping [12] In most OODB algebras, where grouping is an explicitly supported operator and can appear in any place in an algebraic form, any form of query nesting can be unnested by promoting the inner queries one level up in the query nesting hierarchy [3, 4]. This results to a large flat join, which is the concatenation of all the joins in every level in the nested query. Furthermore, all unnesting methods proposed in the literature introduce additional operators, such as outer joins and grouping, thus increasing the number of operators to be ....

S. Cluet and G. Moerkotte. Nested Queries in Object Bases. In Fifth International Workshop on Database Programming Languages, Gubbio, Italy, September 1995.

....it is impossible to transform arbitrary nested queries into flat join queries. As a solution, we introduced the nestjoin operator. In [18] we described a general approach to handle nested queries; here, we are more concrete and present a translation algorithm. Related to our work is that of [5], in which optimization of nested O 2 SQL queries is discussed. In Section 2, we briefly describe the language used and in Section 3 we discuss our approach to the transformation of nested OSQL queries. Next, in Section 4, the main steps of the algorithm are described, and a basic set of rewrite ....

....a nestjoin does not suffer from data replication, but is not commutative like the regular join. object models usually are orthogonal languages; the problem of choosing an algebra for, and of translation into the algebra of such a language is much more complicated. The work presented in [5] and [6] has much in common with ours. In [6] a binary grouping operator is defined that differs slightly from the nestjoin in the sense that the join function is applied to the set of matching right hand operand tuples, not to the elements themselves. This has as a consequence that nested ....

Cluet, S. and G. Moerkotte, "Nested Queries in Object Bases," Proceedings Fourth International Workshop on Database Programming languages, New York, Sept. 1993.

....derive these operators from the unary operator # introduced in section 3. 1, and thus do not produce an (implicit) Cartesian product (in other object oriented algebras this is not always the case, see e.g. 25] on the other hand, our map operator is comparable to the operator denoted by # a:e in [9]) The operators flat and map are to be considered as duals of each other with regard to set nesting, and project and map are to be considered as duals of each other with regard to tupling. A VQL query of the form ACCESS expression (x 1 , x n ) FROM x 1 IN C 1 , x n IN C n WHERE ....

....matching. In this paper we have excluded the issue of nested queries, which is of considerable interest for semantic query optimization based on equivalences, as many equivalences give rise to rules involving nested queries. Some interesting transformation rules for nested queries can be found in [9]. A completely different approach to query optimization in the presence of methods can be found in the REVELATION project [12] objects are asked to reveal the implementation of methods during query optimization. This differs from our approach as we are not interested in the imple mentation ....

S. Cluet, G. Moerkotte: "Nested Queries in Object Bases", Proc. DBPL4, Manhattan, New York City, August 30th -- September 1st, 1993.

....operations over multiple collection types, aggregates, and quantifiers in a similar way, resulting in a uniform way of unnesting queries, regardless of their type of nesting. 1 Introduction There are many recent proposals on OODB query optimization that are focused on unnesting nested queries [9, 8, 6, 7, 19]. Query nesting appears more often in OODB queries than in relational queries, because OODB query languages allow complex expressions at any point in a query. Current OODB systems typically evaluate nested queries in a nested loop fashion, which does not leave many opportunities for optimization. ....

....Since OODB queries are far more complex than relational queries, it is more crucial to express the unnesting transformations in a formal algebra that will allow us to prove the soundness and completeness of these transformations. The first work with that goal in mind was by Cluet and Moerkotte [9, 8], which covered many cases of nesting, including nested aggregate queries, and validated all the transformations. Their work was extended by Claussen et al. [7] to include universal quantification. Our work extends previous work in two ways. First, our unnesting algorithm is not only sound, but it ....

[Article contains additional citation context not shown here]

S. Cluet and G. Moerkotte. Nested Queries in Object Bases. In Fifth International Workshop on Database Programming Languages, Gubbio, Italy, September 1995.

....(E 2 ) objects, which is exactly what is needed for the evaluation of queries with nesting in the select clause: E 1 Delta x;y:f(x) p(x;y) c(x;y) g E 2 = ff(x) Phi hg = fc(x; y) j y E 2 ; p(x; y)gi j x E 1 g See [SABdB94] for a detailed discussion of the nestjoin s characteristics. CM93] achieves functionality similar to the nestjoin by introducing a binary grouping operator. The nestjoin pattern matches our query after we have extracted the uncorrelated subquery via the new rule. As before, we annotate this fact by replacing exactly those parts of the comprehension that can be ....

Sophie Cluet and Guido Moerkotte. Nested Queries in Object Bases. In Proceedings of the 4th Int'l Workshop on Database Programming Languages (DBPL), September 1993.

....manipulation of nested queries by allowing tuples and objects to refer to sets and to each other. This potentially introduces data dependencies into queries, complicating their transformation as we later show. There has been much progress in nested query optimization [24] 17] 20] 30] 31] [12], 14] But nested queries tend to be fairly large and rules for them tend to lack generality or have especially complex head and body routines. As a result, these transformations are rarely implemented as instances of rules, and when they are, the rules are complex and difficult to reason ....

....transformations that further demonstrate the expressive power we get from a KOLA based rule language. A great deal of research has been done in nested query optimization, but typically this research makes it into practice with complex rules that are difficult to formalize and reason about (e.g. [12] and [20] or with transformations expressed informally over query languages (e.g. 24, 17, 31] 4.1 Hidden Join Queries The class of queries we consider are hidden joins; nested queries that (like join queries) pair objects that are taken from two sets and that satisfy some relationship. ....

[Article contains additional citation context not shown here]

S. Cluet and G. Moerkotte. Nested queries in object bases. In Proc. 4th Int'l Workshopon DatabaseProgrammingLanguages,NY, NY, August 1993. Springer-Verlag.

....of collections, and nesting of query expressions. 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] However, there very few proposals on query optimization in the presence of object identity and destructive updates, features often supported by most realistic OODB languages. In earlier work [FM98, FM95b, ....

S. Cluet and G. Moerkotte. Nested Queries in Object Bases. In Fifth International Workshop on Database Programming Languages, Gubbio, Italy, September 1995.

....querying. Object complexity makes it possible to pose queries with lengthy path expressions or that are nested in ways not possible over relations. Path expression optimization has been considered in [KM90a, KM90b] and [Ber91] Optimization of Object Oriented nested queries has been considered in [CM93] and [CZ96] Methods in queries make it necessary to reconsider ways to index [MS86, Hwa94] and to consider the order in which predicates should be evaluated on data [HS93, Hel94, KMPS94, SPMK95] Many areas of querying impacted by objects have been well studied, but as far as we know, ....

Sophie Cluet and Guido Moerkotte. Nested queries in object bases. In Proc. 4th Int'l Workshop on Database Programming Languages, New York, New York, August 1993. Springer-Verlag.

....as E M :A. We illustrate the process in figure 1 with an ODMG [Cat96] schema and query (in OQL) and their translations into CoDi. This example features a class and the representation of a relation in (naturally extended) ODL. Note that CoDi can represent directly dependent joins (see [SZ90, CM93] Equivalence laws In figure 2 we show the basic laws used in CoDi. Some of these laws are derived from the theory of monads and monad algebras and the extensions we worked out in [BNTW95, LT97] We note that (sng,fi, assoc) hold for all monads, null) is true for monads with a nullary ....

S. Cluet and G. Moerkotte. Nested queries in object bases. In Proc. DBPL, pages 226--242, 1993.

....above (with extensions) as its translation target. Section 4 summarizes. 2 Algebraic Representations for OQL Having the instruments of NRA at hand, there is a tendency to view OQL queries as advanced SQL queries, with an explicit emphasis on the efficient translation of nested subqueries [11,6,15]. 2.1 Nested selects The following select from where clause is understood as the basic building block of complex queries (let e denote e 1 ; e n ) select struct(a 1 :e k1 ; a k :e kk ) from E 1 as e 1 ; En as e n where p(e) The obvious algebraic translation would be ....

....1 where p(e 1 ) The above form immediately leads to a nested projection if we apply the above algebraic translation scheme. Execution of such plans often results in inefficient nested loop processing. Consequently, recent work proposed non standard join operators such as binary grouping ( Gamma , [6]) hierarchical joins [14] or the nestjoin ( Delta, 15] which we will look upon more closely in the following. Actually, the above query is implemented by a single nestjoin which performs a join over predicate p 0 and a grouping with regard to function f simultaneously: oe[e 1 :p(e 1 ) E ....

Sophie Cluet and Guido Moerkotte. Nested Queries in Object Bases. In Proceedings of the 4th Int'l Workshop on Database Programming Languages (DBPL), September 1993.

....of the register set and attempts to apply generalized register management techniques to manage the cache. In the database world, Lieuwen[63] has found that performing compiler style analyses on database programming language loops allows those loops to be turned into joins. Cluet Moerkotte [21], in their work on nested queries have found dependency information to be very useful. These parallels make us confident that our techniques will prove useful. 2.6 Buffer Management Buffer management has always been a factor that affects the performance of database systems[29] Most work on ....

Sophie Cluet and Guido Moerkotte. Nested queries in object bases. In Beeri [7], pages --.

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Sophie Cluet and Guido Moerkotte. Nested queries in object bases. In Proceedings of the Fourth International Workshop on Database Programming Languages - Object Models and Languages, pages 226-242, New York City, NY, USA, 1993.

....but offers some optimization possibilities that should be exploited. The main idea is thus to integrate schema lookup and object base lookup in an algebra, and thereby be able to apply optimization techniques in a homogeneous fashion to both lookups. For this, 14] extends the algebra of [15] with two new operators, S inst and D inst, that instantiate GPE s from a schema and a data perspective. We do not define the algebra here, simply gives an intuition, using an example, of the optimization process and of its potential. Readers are referred to [14, 12] for more details. The example ....

....the simple value Web is compared with the set of titles of the database documents. Hence, an explicit existential quantifier is introduced in the corresponding OQL query. After this step, the logical query plan given in Fig. 8 is constructed. It consists of several scan operators, three d joins [15], some select and project operators Documents.document d Scan d.section s Scan D Join s.title t Scan D Join groupBy d, OpExists: E G Agg D Join t2 contains Web Select d.title t2 Scan E = true Select t Project Fig. 8. Lorel Plan for Query Q5 as well as a generalized aggregate ....

S. Cluet and G. Moerkotte. Nested queries in object bases. In Proc. Workshop on Database Programming Languages (DBPL), 1993.

....some optimization possibilities that should be exploited. The main idea of our technique is thus to integrate schema lookup and object base lookup in an algebra, and thereby be able to apply optimization techniques in a homogeneous fashion to both lookups. For this, we extended the algebra of [cm93] with two new operators, S inst and D inst, that instantiate GPEs from a schema and a data perspective. Let us consider the algebraic translation of Query 2.1 shown on the left side of Figure 1. Formal definitions of the S inst and D inst operators along with syntactical definitions of GPEs, path ....

....Let us consider the algebraic translation of Query 2.1 shown on the left side of Figure 1. Formal definitions of the S inst and D inst operators along with syntactical definitions of GPEs, path and patterns are given in [chr96] The definition of the standard algebraic operators can be found in [cm93]. We now explain this translation. Operation (1) allows us to view Encyclopedia as a set of tuples with one attribute v1. This feature is essential to the algebra whose operators are, for the most part, defined on set of tuples. This gives nice properties to our operators. At the end of (1) we ....

S. Cluet G. Moerkotte. Nested Queries in Object Bases. In Proceedings International Workshop on Database Programming Languages, 1993.

....operations, tree creation and access operations. painter [ name [ concat( Van , Gogh ) contemp [ 1890 1900) works [ vg artist painted ] painter [ name [ Van Gogh ] contemp [ false ] works [ ci ] ffl It directly provides support for nested queries. Nested queries [14, 20] are very convenient to deal with nested structures like in XML. ffl It facilitates language s extensions. The ability to call externally defined functions is an important feature to be able to query [23] and integrate [19] XML. Closure under composition allows to add any new side effect free ....

S. Cluet and G. Moerkotte. Nested queries in object bases. In Proceedings of International Workshop on Database Programming Languages, pages 226--242, New York City, USA, Aug. 1993.

.... two simpli cations can be combined in case neither p nor q depends on e 1 : Simpli cation 9 If neither p nor q depend on e 1 , that is, e 1 does not occur in either of p or q query classes 1, 3, 9, and 11 of Table 1 , then their evaluation is independent of e 1 and by dependency based rewriting [CM93] the query can be rewritten to if for all e 2 in select e 2 from e 2 in E 2 where p: q then E 1 else ; 4.2 Example Applications of the Rewriting Rules In order to demonstrate the viability of our rule based query rewriting approach, we give an example for query class 8 p(e 1 ) and q(e 1 ; e ....

S. Cluet and G. Moerkotte. Nested queries in object bases. In Proc. Int. Workshop on Database Programming Languages, 1993.

....introduces some preliminaries, namely the algebra and the translation of SQL like queries into the algebra. The core of the paper is contained in Section 3. It represents the classification of oo nested queries together with the algebraic equivalences used for unnesting. We review some results of [8] and introduce new unnesting techniques for those cases which could not be unnested so far. In Section 4, we briefly present techniques for unnesting nested queries with quantifiers. More on the treatment of quantifiers can be found in [9] Section 5 concludes the paper. 2 Preliminaries 2.1 ....

....applied to other languages like GOMql [16] or Excess [4] As a matter of fact, O 2 SQL is a subset of the oo standard query language as defined in [5] The schema on which the queries are defined represents a company. It can be easily inferred from the queries and, hence, we will not detail it. In [8], we showed the importance of factoring out constant or locally constant subqueries as well as common subexpressions. For this purpose, we introduced a phase preceding the optimization process. This phase called dependency based optimization transforms the SQL like query by introducing ....

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S. Cluet and G. Moerkotte. Nested queries in object bases. In Proc. Int. Workshop on Database Programming Languages, pages 226--242, 1993.

....been devoted to optimizing object queries. Special index structures for path indexes [2, 12, 18, 20] class indexes [17, 16] and function materialization [11] have been proposed. Logical optimization techniques have been developed. They cover path evaluation [1, 13] factorization [5] unnesting [6, 19], optimization in the presence of expensive methods [9, 15] disjunctions [14] or aggregates [7] Looking at all the effort, it is surprising, that, in the context of query optimization, class hierarchies did not receive special attention. The only special support developed so far are index ....

S. Cluet and G. Moerkotte. Nested queries in object bases. In Proc. Int. Workshop on Database Programming Languages, 1993.

....several bugs in this approach have been detected and corrected [9, 11, 13] The main point is to use an outer join instead of a regular join. Nevertheless, the main idea join, group, aggregate still remains the same and is even today the only known improvement over nested loops [7, 16, 17]. Let us call this approach A G J. Lately, it was proposed to exchange grouping and aggregate operations with joins [19, 18, 20, 5, 6] This work is orthogonal to our s in that our method can be used to implement the grouping and aggregate operations used there. Consider the performance of this ....

....expression builds a bulk of tuples of a single attribute x whose values are the original element x of a bulk type X. Hence, any bulk( instance is turned into a bulk( x : instance. The main motivation behind these definitions is that it is quite convenient to deal with bulks of tuples only [7, 12]. The last operator needed on bulk types is selection. For a function p : Bool, it is denoted by oe p and has the signature oe p : bulk( bulk( The definition is given by oe p ( oe p (x y) oe p (x) oe p (y) and oe p (bulk(x) bulk(x) for a singleton bulk(x) if p(x) and ....

S. Cluet and G. Moerkotte. Nested queries in object bases. In Proc. Int. Workshop on Database Programming Languages, 1993.

No context found.

Sophie Cluet and Guido Moerkotte. Nested queries in object bases. In Workshop on Database Programming Languages, pages 226--242, 1993.

No context found.

Sophie Cluet and Guido Moerkotte. Nested queries in object bases. In Proceedings of International Workshop on Database Programming Languages, pages 226--242, New York City, USA, August 1993. http://cosmos.inria.fr:8080/cgi-bin/publisverso?what=abstract&query=064.

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