Thomas, S., Fischer, P.: Nested relational structures. In: P. Kanellakis (ed.) The theory of databases, pp. 269 --307. JAI Press (1986)  Home/Search   Document Not in Database   Summary   Related Articles   Check

....fProject A, Project B,Project Cgg . Computing Final Project B Project C Bill Sid2 Physics P100 Final Prac 1 Prac 2 Chemistry CH200 Test A Experiment 1 Test B Experiment 2 1 Figure 18: A nested relation. We now introduce the nest and unnest operators for nested relations as defined in [38]. Definition 22 Let Y be a nonempty proper subset of N (S) Then the operation of nesting a relation on Y , denoted by Y (r ) is defined to be a nested relation over the scheme (N (S) Gamma Y ) fY g and a tuple t 2 Y (r ) iff: i) there exists t 1 2 r such that t[N (S) Gamma Y ] ....

....define the total unnest of a nested relation r , denoted by ) as the flat relation defined as follows. Definition 24 (i) if r is a flat relation then ) r (ii) otherwise ) fY g (r ) where fY g is a higher order attribute in the NRS for r . It can be shown [38] that the order of unnesting is immaterial and so (r) is uniquely defined. Also, we need the following result from [38] Let us denote the NRS of nested relation r by N (r ) Lemma 2 For any nested relation r and any Y N (r ) fY g ( Y (r ) r . We note the well known ....

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S.J. Thomas and P.C. Fischer. Nested relational structures. In P. Kanellakis, editor, The theory of databases, pages 269 --307. JAI Press, 1986.

....Web site. In addition to formally defining nested tables with internal variations, this paper also formally defines a set of query operations for semistructured data represented as an internally varying nested table. We base this set of operations on several proposals found in the literature [1, 8, 18, 29, 30], particularly on the algebra proposed by Colby [8] As a further contribution, this paper Ii . i [ 2 2 6 ; i [ ....

....in Figure 2. If we project on the column Item ist, we cannot group the resulting instances in a table because of the different structure in each variation. We would thus need an additional level of nesting to create a single table. Nest (v) Similar to the operation proposed by Thomas and Fischer [30], our nest operation has two distinct semantics. When applied to a single column, this operation groups the values in the column that are associated with equal values occurring in all other columns. Otherwise, when the nest operation is applied to a set of columns, it creates a new table scheme ....

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THOMAS, S. J., AND FISCHER, P. C. Nested Relational Structures. Advances in Computing Research 3 (1986), 269-307.

....database late an update on an XML view to a set of updates on the underlying relations without introducing additional updates to the XML view. To simplify the problem yet capitalize on the use of XML to capture nested relations, we consider XML views as defined by the nested relational algebra [23, 14]. The nested relational algebra contains the classical relational algebra operators (#, #, #, ##, as well as the nest (#) and unnest ( operators. There are several reasons for considering this algebra: First, there is a straightforward mapping between nested relations and XML views in ....

....this view because we do not have the primary key of the Papers relation. However, for XML views defined by general nested relational algebra (NRA) queries little can be said about updatability. Some general NRA queries can be rewritten to nest last relational form using the rewrite techniques of [23]. However, there are others that cannot be rewritten and these remain an open problem. We will therefore focus in this paper on views produced by nest last relational queries, and well nested project select join queries. The rest of this paper is organized as follows. In section 2 we define what ....

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S. J. Thomas and P. C. Fischer. Nested relational structures. Advances in Computing Research, 3:269--307, 1986.

....to translate an update on an XML view to a set of updates on the underlying relations without introducing additional updates to the XML view. To simplify the problem yet capitalize on the use of XML to capture nested relations, we consider XML views as defined by the nested relational algebra [24, 15]. The nested relational algebra contains the classical relational algebra operators (#, #, #, ##, as well as the nest (#) and unnest ( operators. There are several reasons for considering this algebra: First, there is a straightforward mapping between nested relations and XML views in ....

....this view because we do not have the primary key of the Papers relation. However, for XML views defined by general nested relational algebra (NRA) queries little can be said about updatability. Some general NRA queries can be rewritten to nest last relational form using the rewrite techniques of [24]. However, there are others that cannot be rewritten and these remain an open problem. We will therefore focus in this paper on views produced by nest last relational queries, and well nested project select join queries. We further assume that the underlying relational database is well designed ....

[Article contains additional citation context not shown here]

THOMAS, S. J., AND FISCHER, P. C. Nested relational structures. Advances in Computing Research 3 (1986), 269--307.

....between NF and XML, one approach to the mapping from relational databases to XML could be the use of a database engine capable of executing NF operators. Such an engine should implement at least the operators of the classical relational algebra as well as the NF specific nest operator [JAE 82, THO 86] 24 User Application SQL SELECT statements FIGURE 3.5 uR2X Wrapper However, there are no DBMSs that implement efficiently the NF operators. As we are aiming at efficiency of query execution, we prefer an implementation method that relies on relational database engines widely ....

THOMAS, S.; FISCHER, P. C. Nested relational structures. Advances in Computing Research, v.3, p.269--307, 1986. 61

....(i.e. a structural condition) The projection operation is similar to the projection operation defined in the relational algu ra. We can say that this operation horizontally red ces a table by keeping only the col mns specified by the ser. Similar to what was proposed by Thomas and Fischer [5], the nest operation has two distinct semantics. When applied to asing le col mn, this operation g1 ps the val es in the col mn that are associated with eq al val es occ rring in other col mns. Otherwise, it creates a new internal table that gu ps the val es of these col mns and, conseq ....

....val es occ rring in other col mns. Otherwise, it creates a new internal table that gu ps the val es of these col mns and, conseq ently, g6]664uT a new level ofnesting in the table. The unnest operation is the inverse of the nest operation. It also has two distinct semantics, according to [5], and it is only valid for col mns containing list of atoms or an internal table. If it is applied to a list of atoms, it will ng ro p its elements, i.e. it will split them into di#erent rows of the table. Otherwise, if it is applied to an internal table it will eliminate a level of nesting ....

Thomas, S. J., and Fischer, P. C. Nested Relational Structures. Advances in Computing Research 3 (1986), 269--307. 721

....order attributes using ( is convenient in our formalism since it highlights their internal structure. A more user friendly notation would be to give each higher order attribute, R(T i ) a higher order name determined by the user as it is done in the nested relational formalisms found in [28, 31]. 10 EXAMPLE 2.1. Let T be the scheme tree over W = AIRLINE, AIR CODE, FLIGHT NO, PASSENGER, CREW, AIRPORT, PORT CODE , shown in Fig. 1.1; thus, we have S(T) W. Moreover, we have the NRS R(T) AIRLINE AIR CODE (FLIGHT NO (PASSENGER) CREW) AIRPORT PORT CODE) A flat relation scheme ....

....# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # FIG. 2.6. The nested relation r 3 over R(T 3 ) in a minimal way as is done in the minimal algebras found in [31, 34]. That is to say it corresponds naturally to the standard union operator whereby tuples in a nested relation are considered as indivisible units. The rest of the operators of the null extended algebra are defined in a maximal way, i.e. they are defined recursively to take into account the ....

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S.J. THOMAS AND P.C. FISCHER, Nested relational structures, in "Advances in Computing Research," Vol. 3, (P.C. Kanellakis and F. Preparata, Eds.), JAI Press, Greenwich, 1986, pp. 269307.

....and iteration facilities. KEY WORDS: nested relations, null values, null extended algebra, faithful extended algebra operators, precise extended algebra operators ############### Appeared in Fundamenta Informaticae, Vol. 19, pp. 303 343, 1993. 2 1. Introduction The nested relational model [1, 2, 8, 13, 15, 16, 19, 20, 21, 22, 23, 26, 28] was developed in order to extend the applicability of the relational model [5, 18, 27] to more complex, nonbusiness applications such as CAD, image processing and text retrieval [2] Nested relations can model complex data directly by recursively defining values of attribute domains to be either ....

....and text retrieval [2] Nested relations can model complex data directly by recursively defining values of attribute domains to be either flat relations in first normal form [5, 18, 27] or nested relations. Recently many extended algebras have been suggested for the nested relational model [1, 3, 6, 8, 10, 15, 16, 17, 21, 22, 23, 26, 28]. From these extended algebras only those of Roth et al. 22] Levene [15] and Levene and Loizou [16] have comprehensively incorporated null values into the nested relational model; Roth et al. 22] deal with a subclass of nested relations, whilst Levene and Loizou [16] deal with an extension of ....

[Article contains additional citation context not shown here]

S.J. Thomas and P.C. Fischer, Nested relational structures. In: P.C. Kanellakis and F. Preparata (Eds.), Advances in Computing Research, Vol. 3. JAI Press, Greenwich, 1986, pp. 269-307.

....from Amazon Web site. In addition to formally de ning nested tables with internal variations, this paper also formally de nes a set of query operations for semistructured data represented as internally varying nested table. We base this set of operations on several proposals found in literature [1, 5, 14, 22, 23], particularly on the algebra proposed by Colby [5] As a further contribution, this paper also describes QSByE (Querying Semistructured data By Example) 11] which shows 3 ProductList Store Info Popular Music Title Artist AudioType Wingspan (Hits History) Paul McCartney Audio CD . ....

....table in Figure 2. If we project on the column Info, we cannot group the resulting instances in a table because of the di erent structure in each variation. We would thus need an additional top level of nesting to create a single table. Nest ( Similar to what was proposed by Thomas and Fischer [23], the nest operation has two distinct semantics. When applied to a single column, this operation groups the values in the column that are associated with equal values occurring in other columns. Otherwise, when the nest operation is applied to a set of columns, it creates a new table scheme that ....

[Article contains additional citation context not shown here]

Thomas, S. J., and Fischer, P. C. Nested Relational Structures. Advances in Computing Research 3 (1986), 269-307.

....and their characterization by a new family of dependencies, and furthermore, they developed a polynomial time algorithm to test if a structure is a one level nested relation. Thomas and Fischer generalized their work on the one level model and allowed nested relations of arbitrary, but fixed depth [Tho86]. In [RKS86] Roth, Korth and Silberschatz defined a normal form called Partitioned Normal Form(PNF) for nested relation, and also defined algebra and calculus query languages for them; however, their proofs and method were later questioned by Tansel and Garnett [Tag92] Numerous query languages ....

S. Thomas, P. Fischer. Nested relational structures. In Advances in Computing Research III, The Theory of Databases, P.C.Kanellakis, Ed. JAI Press, Greenwich, Conn., 1986.

....nested relation. Jaeschke and Schek [JS82] introduced a generalization of the ordinary relational model by allowing relations with setvalued attributes and adding two restructuring operators, the nest and unnest operators, to manipulate such (one level) nested relations. Thomas and Fischer[TF86] generalized Jaeschke and Schek s model and allowed nested relations of arbitrary (but fixed) depth. The definition of recursively nested relations was also discussed [LS88] On the other hand, various query languages have been introduced for the nested relational model, and extensions have been ....

S. J. Thomas and P. C. Fischer. Nested relational structures. In P. C. Kanellakis, editor, Advances in Computing Research III, The Theory of Databases, pages 269--307. JAI Press, 1986.

....been made in the field of nested relations since the nested relational model was first proposed in 1977 [Mak77] Fisher and Van Gucht [FG85] discussed the one level nested relations and developed a polynomial time algorithm to test if a structure is an one level nested relation. Thomas and Fischer[TF86] generalized the one level nested relations to nested relations of arbitrary but finite depth. The definition of recursively nested relations was also discussed [LS88] Various query languages have been introduced for the nested relational model, and extensions have been proposed to practical ....

S. J. Thomas and P. C. Fischer. Nested relational structures. In P. C. Kanellakis, editor, Advances in Computing Research III, The Theory of Databases, pages 269--307. JAI Press, 1986.

....zaza mary toto mary zaza fred nini A P C ff sam toto ff sam zaza ff mary toto ff mary zaza fi fred nini S C ff toto ff zaza fi nini P S sam ff mary ff fred fi Figure 3: Abstraction. literature. Abstraction corresponds to such concepts as grouping over sets [BNR 87] nesting [TF86] set valued functions [AG91] and set valued object assignments [AK89] The transformation language with relational statements (giving us firstorder logic) new (giving us tuple id creation) abstr (giving us set id creation) and recursion is essentially equivalent to the IQL language, ....

S. Thomas and P. Fischer. Nested relational structures. In P. Kanellakis, editor, The Theory of Databases, pages 269--307. JAI Press, 1986.

....concepts in the database context are object identity and complex modelling. In this paper, we concentrate on the latter one. General complex object databases were presented in [1, 5] A particular and well known model supporting complex objects is the nested relational database model [17, 19]. It is an extension of the relational database model in which a table element can be an atomic value, as in ordinary relations, but also a nested relation in turn. Complex structures can be represented more naturally using nested relations. The paper is organized as follows. Section 2 introduces ....

S. Thomas, P. Fischer: "Nested relational structures", The theory of databases, P. Kanellakis, ed., pp. 269--307, JAI Press, 1986.

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Thomas, S., Fischer, P.: Nested relational structures. In: P. Kanellakis (ed.) The theory of databases, pp. 269 --307. JAI Press (1986)

No context found.

S.J. Thomas and P.C. Fischer. Nested relational structures. In P. Kanellakis, editor, The theory of databases, pages 269 --307. JAI Press, 1986.

No context found.

S. J. Thomas and P. C. Fischer. Nested relational structures. In Advances in Computing Research: The Theory of Databases, pages 269--307, London, England, 1986. JAI Press.

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S. J. Thomas, P. C. Fischer, Nested relational structures, in "Advances in Computing Research: The Theory of Databases," JAI Press, 1986.

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S. J. Thomas, P. C. Fischer, Nested relational structures, in "Advances in Computing Research: The Theory of Databases," JAI Press, 1986.

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S.J. Thomas and P.C. Fischer. Nested relational structures. In Advances in Computing Research: The Theory of Databases, pp 269--307, 1986.

No context found.

S. J. Thomas and P. C. Fischer, "Nested Relational Structures," in Advances in Computing Research, vol. 3, 1986, pp. 269-307.

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S.J. Thomas and P.C. Fischer. Nested relational structures. In P. Kanellakis, editor, The theory of databases, pages 269 --307. JAI Press, 1986.

No context found.

S.J. Thomas and P.C. Fischer. Nested relational structures. In P. Kanellakis, editor, The theory of databases, pages 269 --307. JAI Press, 1986.

No context found.

S.J. Thomas and P.C. Fischer. Nested relational structures. In P. Kanellakis, editor, The theory of databases, pages 269 --307. JAI Press, 1986.

No context found.

S.J. Thomas and P.C. Fisher, 'Nested relational structure', in P.C. Kanellakis (ed.), Advances in Computing Research III, The Theory of Databases, JAI Press,

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