J. D. Ullman, Principles of Database Systems (Comput. Sci. Press, Potomac, Md., 1982).  Home/Search   Document Not in Database   Summary   Related Articles   Check

....the buffer size range [3. 5] may be calculated in constant time. 5.2 Experiment testbed We ran several experiments to test the effectiveness of the implemented algorithms for query optimization. The machine used for the experiments was a DECstation 3100. The algorithms were run on tree queries [Ull82] consisting of equality joins only. The size of these queries, which were generated randomly, ranged from 1 to 20 joins. They were tested with a randomly generated relation catalog where relation cardinalities ranged from 1000 to 100000 tuples, and the numbers of unique values in join columns ....

Ullman JD (1982) Principles of Database Systems. Computer Science Press, Rockville, MD

....when rewriting a candidate TSS network N are (a) to exploit the clustering of the selected fragments and (b) to minimize the sizes of the intermediate results. The optimizer calculates the cost of evaluating a rewriting R applying the Wong Yusefi algorithm and the cost estimations presented in [22]. The evaluation starts from the leaves which are the small relations and the join paths meet on one or more meeting fragments. The most e#cient join method on the meeting fragments is the index join. Notice that the sizes of the non free TSS s, which are needed in the cost calculation, are ....

....the number of fragments, but in practice it is fairly small, given that the size of the candidate TSS networks is bound and the number of fragments that contain each edge of the schema graph is limited. Hence the optimizer can e#ciently select an optimal rewriting with respect to the cost model of [22]. 7Execution The execution module of XKeyword aims at providing fast response time to keyword queries. Depending on the presentation method selected (see Section 3.1) we follow a di#erent execution approach. Web search engine like presentation. In the case of the web search engine like ....

J. D. Ullman. Principles of Database Systems, 2nd Edition. Computer Science Press, 1982.

....include (fragments of) syntax trees in relations. 3.2.2. A Relational Calculus In relational algebra, queries are expressed by applying specialized operators to relations. In relational calculus, queries describe a desired set of tuples by specifying the predicate the tuples must satisfy. See [42] for a complete coverage of this distinction. As an experiment, we define a little relational calculus (let s call it RSCRIPT) with the usual operators on bags and sets such as union, elem (is element of) equality) and more. We also use bag and relation formers that resemble list ....

J.D. Ullman. Principles of Database Systems, Second Edition. Computer Science Press, 1982.

....the minimum number of SQL queries needed to answer to the keyword query. Furthermore, DISCOVER operates directly on the databases, so it does not have a main memory space limitation. The work of the Candidate Network Generator reminds of algorithms for answering queries on universal relations [Ull82] However there are many important differences between universal relations and DISCOVER: First, there is the obvious difference that the user of a Universal Relation (UR) needs to know the attributes where the keywords are, in contrast to the user of DISCOVER. Second, DISCOVER creates efficient ....

....by the Plan Generator is a form of multi query optimization [Sel88, Fin82, RSSB00] However the candidate networks in DISCOVER have special properties that allow us to develop a more straightforward and efficient algorithm. The first property is that the candidate networks have small relations [Ull82] as leaves, which dramatically prunes the space of useful common subexpressions when applying the Wong Yusefi algorithm [Ull82] Second, the candidate networks are not random queries, but share common subexpressions by the nature of their generation as we see in Section 4. The techniques of ....

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Jeffrey D. Ullman. Principles of Database Systems, 2nd Edition. Computer Science Press, 1982.

....[Miller98] R. Miller: Using Schematically Heterogeneous Structures . Proceeedings of the ACM [SW95] K. Sagonas, D. Warren: Efficient Execution of HiLog in WAM based Prolog Implementations . Proceedings on the twelth International Conference on Logic Programming, Tokyo, Japan 1995: 349 363. [Ullman82] Jeffrey D. Ullman: Principles of Database Systems , 2nd Edition. Computer Science Press 1982, ISBN 0 914894 36 6. VP97] V. Vassalos, Y. Papakonstantinou: Describing and Using Query Capabilities of Heterogeneous Sources . Proceedings of the 23 d VLDB Conference, Athens Greece, 1997. VRG98] ....

Jeffrey D. Ullman: "Principles of Database Systems", 2nd Edition. Computer Science Press 1982, ISBN 0-914894-36-6.

.... such as relational algebra, to be executed on the extensional database (fact base) This is a simple process for Horn clauses containing only nonrecursive predicates with simple variables, inasmuch as these rules basically correspond to the derived joinselect project views of relational databases [21]. Horn clauses, however, contain two powerful constructs not found in the relational calculus: one is recursion, which, e.g. entails the computation of closures, the other is general unification, which, via the use of function symbols, can be used to support complex and flexible structures (not ....

J.D. Ullman, Principles of Database Systems (Computer Science Press, Rockville, MD, 1982).

.... of the set theoretic properties of relations in the presence of nulls represents an open problem and a very important one since set theory provides the bedrock on which the relational model is built and a complete relational algebra includes the operations of set union and difference [22]. Interesting notions relating to the treatment of nulls under the unknown inter pretation have also been proposed by other authors Ill, 16, 241. We discuss them later. Our more immediate concern is to illustrate the many facets of the problem at hand. Among these we find the nonexistent ....

J. D. ULLMAN, "Principles of Database Systems," 2nd ed., Computer Science Press, Potomac, Md., 1983.

....multivalued dependency and join dependency. This research utilized the functional and multivalued dependency relationships in forming the D table. Functional dependencies describe the relationship between two attribute sets. Formally, this relationship can be expressed by the followin definition [16]: let R(A 1, A 2 . A n) be a universal relation scheme, and let X and Y be subsets of A 1, A 2 . An . We say X Y, read X functionally determines Y or Y functionally depends on X if whatever relation r is the current value for R, it is not possible that r has two tuples that ....

.... scheme R, let X and Y be subsets of R, we say that X Y ( Denote X multidetermines Y ) if given values for the attributes of X there is a set of zero or more associated values for the attributes of Y, and this set of Y values is not connected in any way to values of the attributes in R X Y [16]. Consider the following relation schemes of a university database: RI: FACULTY ( faculty ssn, name, depart name, course # ) STUDENT ( student ssn, name, birth date, class stand, major, GPA, area of interest ) R3: COURSE ( depart name, course #, text ) COMPANY ( company name, area of ....

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Ullman, J.D., Principles of Database Systems, 2nd Edition, Computer Science Press, Rockville, MD 1982.

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J. D. Ullman, Principles of Database Systems (Comput. Sci. Press, Potomac, Md., 1982).

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J.D. Ullman, "Principles of Database Systems", Computer Science Press, 1982.

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J. D. Ullman. Principles of Database Systems. Computer Science Press, 1982.

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Ullman, J.D, Principles of databases systems, Second Edition, pp. 207-209, Computer Science Press, 1982.

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J. D. Ullman. Principles of Database Systems. Computer Science Press, Rockville, 1982.

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Ullman, J.D., `Principles of Database Systems', Computer Science Press, Inc., (1982).

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J. D. Ullman. Principles of Database Systems, 2 nd edition. Computer Science Press, 1982. 108

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J.D. Ullman. Principles of Database Systems. Computer Science Press, 1982.

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J.D. Ullman. Principles of Database Systems, 2nd edition. Computer Science Press, Potomac, Maryland, 1982.

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J. Ullman. Principles of Database Systems. Computer Science Press, Rockville MD, 1982.

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Ullman, J. D., Principles of Database Systems. Computer Science Press, 2 edition, 1982.

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J. D. Ullman. Principles of Database Systems. Computer Science Press, 1982.

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Jeffrey D. Ullman. Principles of Database Systems, 2nd Edition. Computer Science Press, 1982.

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Ullman, J.D., Principles of Database Systems, Computer Science Press, Rockville, Md., 1982.

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Jeffrey D. Ullman: "Principles of Database Systems", 2nd Edition. Computer Science Press 1982, ISBN 0-914894-36-6.

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J. D. Ullman. Principles of Database Systems, Second Edition. Galgotia Publications (P) Ltd., 1993.

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J. D. Ullman. Principles of Database Systems, Second Edition. Galgotia Publications (P) Ltd., 1993.

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