R. Fagin, A. Mendelzon, and J. Ullman. A simplified universal relation assumption and its properties. ACM Transactions on Database Systems, 7, 1982.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....consider Hobby, which is a redundant object set as explained earlier in Example 5. To illustrate the bidirectional edge requirement, consider the functional edges between Department and Abbreviation We make neither the universal relation assumption nor the universal relation scheme assumption [FMU82,Ken81]. Member Department Grad Student Program Faculty Hobby Grad Student Hobby Hobby Location Abbreviation (a) Noncanonical Faculty Member Department Grad Student Program Faculty Hobby Grad Student Hobby Location Abbreviation has applied for next mail drop off (b) ....

R. Fagin, A.O. Mendelzon, and J.D. Ullman. A simplified universal relation assumption and its properties. ACM Transactions on Database Systems, 7(3):343--360, September 1982.

.... recognized as useful, for instance, are the information preserving joins independently introduced in [13, 25] Also, null values have been found useful in mapping network schemas into relational schemas [15,26,27] in distributed databases, and in ensuring the universal relation assumption [6]. There is a need for integrating these new concepts and ad hoc applications in a complete and consistent framework. This paper presents a new approach that avoids the dilemma of the unknown versus the nonexistent interpretation and provides an etension that preserves two key advantages of ....

R. FAGIN, A. MENDELZON, AND J. ULLMAN, A simplified universal relation assumption and its properties, A CM Trans. Database Systems 7(3)(1982), 343-360.

....the input set of GMVDs. In order to show that the constructed dependency structure H is a perfect map of the input set of GMVDs, it must be demonstrated that the set of all GMVDs inferred from the dependency structure is logically equivalent to the input set of GMVDs. We can adopt the method in [8] to compute all the GMVDs that are logically implied by an acyclic hypergraph structure, as the following theorem suggests. Theorem 2 Let OE be a distribution defined on an hypergraph H. Suppose X and Y are disjoint sets of attributes. Then the GMVD X Gammaffi Y follows logically from OE if and ....

....H. Suppose X and Y are disjoint sets of attributes. Then the GMVD X Gammaffi Y follows logically from OE if and only if Y is the union of some connected components of the hypergraph H with the set of nodes X deleted. The proof of Theorem 2 can be derived in a similar fashion to the one in [8], and will be shown in a more complete paper. Theorem 2 implies that the set of all GMVDs that can be logically inferred from an acyclic hypergraph structure H is given by: fX Gammaffi Y 1 j Y 2 j: jY m j X 2 Lg; where L is the set of J keys of H and the Y i s are the disconnected ....

R. Fagin, A. Mendelzon, and J. Ullman. A simplified universal relation assumption and its properties. ACM Transactions on Database Systems, 7(3):343--360, September 1982.

....provides us with all the advantages of nested relations over flat relations. 5 1. INTRODUCTION A database model provides logical data independence if changing the database at the conceptual level does not affect the user s view of the database. The classical universal relation model (UR model) [3, 10, 24, 25, 26, 27, 30, 32, 35] endeavours to achieve logical data independence in the flat relational model [8, 33] by allowing the user to view the database as if it were composed of a single flat relation. To this end, the user is provided with a UR interface [32] with all the semantics embedded into the attributes ....

R. FAGIN, A.O. MENDELZON, AND J.D. ULLMAN, A simplified universal relation assumption and its properties, ACM Trans. Database Systems 7, No. 3 (1982), 343-360.

....to envision many thousands of resource agents distributed over the Internet, dynamically coming and going, each claiming coverage over part of this ontology. An assumption that underlies all the algorithms in this paper is that domain ontology may be viewed as a unique Universal Relation[16] 17][7][12] This is true for the example movie schema and this Universal Relation appears in table 4. Note that this assumption does not imply that a Universal Relation is actually used to model ontologies 4 or for query processing. The Universal Relation assumption is merely a convenient way of ....

R. Fagin and J.D. Ullman A. Mendelzon. A simplified universal relation assumption and its properties. Rj2900, IBM Research Labs, San jose, California, 1980.

....as well as a practical point of view. In some contexts, acyclic hypergraphs gain special attention. e.g. in relational database theory acyclic hypergraphs (also called tree schemes) were introduced in [8] and later used by many authors (cf. 53, 30] especially in relational database design, cf. [2, 4, 5, 17]. Several NP complete problems on hypergraphs become polynomial for acyclic hypergraphs [57] Since it is not straightforward to carry over the definition of a cycle from graphs to hypergraphs, there are many notions of acyclicity in a hypergraph, cf. 16, 18, 7] We refer to ff , fi , fl , and ....

R. Fagin, A. Mendelzon, and J. Ullman, A simplified universal relation assumption and its properties, ACM Trans. on Database Syst., 7 (1982), pp. 343--360.

.... Similar to graph theory, the notion of acyclicity is appealing in hypergraph theory from a theoretical as well as a practical point of view, and for some practical problems acyclic hypergraphs gain special attention, e.g. in the design of relational database schemata [BDM81, BFM 81, BFMY83, FMU82] Several NP complete problems on hypergraphs become polynomial if they are restricted to acyclic hypergraphs [Yan82] Since it is not straightforward to carry over the definition of a cycle from graphs to hypergraphs, there are many notions of acyclicity in a hypergraph, cf. Fag83, FV84, ....

R. Fagin, A.O. Mendelzon, and J.D. Ullman. A simplified universal relation assumption and its properties. ACM Trans. on Database Syst., 7(3):343--360, 1982.

....in a relation scheme of the given database scheme, we also assume that each relation scheme is in BCNF with respect to the given FDs. These assumptions are justified as follows. First, in Section II B, we have already mentioned the importance of acyclic database schemes. Second, as stated in [FMU82], most FDs that are relevant for data structuring are embedded in some relation schemes of the given database scheme. Furthermore, most FDs that are derived from the semantic data models that we use in [ME96] ME98] are indeed embedded in some relationship sets which roughly correspond to ....

R. Fagin, A. O. Mendelzon, and J. D. Ullman. A simplified universal relation assumption and its properties. ACM Transactions on Database Systems, 7(3):343--360, September 1982.

....to envision many thousands of resource agents distributed over the Internet, dynamically coming and going, each claiming coverage over part of this ontology. An assumption that underlies all the algorithms in this paper is that domain ontology may be viewed as a unique Universal Relation[16] 17][7][12] This is true for the example movie schema and this Universal Relation appears in table 4. Note that this assumption does not imply that a Universal Relation is actually used to model ontologies 4 or for query processing. The Universal Relation assumption is merely a convenient way of ....

R. Fagin and J.D. Ullman A. Mendelzon. A simplified universal relation assumption and its properties. Rj2900, IBM Research Labs, San jose, California, 1980.

....attributes are referenced in that sentence. Different approaches for simplifying query formulation can be found in the literature. In the universal relation approach, query inference is addressed by building a derived relation which combines all the relations in the database through natural joins [3]. On the other hand, the universal relation calls for requirements not always satisfied in practical applications [4] and generates a fixed sight of the database, on whose structure the user cannot intervene. In [7] derived relations are computed following a graph theoretic approach. Each ....

R. Fagin, A.O. Mendelzon and J.D. Ullman. A simplified universal relation assumption and its properties. ACM Trans. Database Syst. 7, 3, 343-360 (1982).

....paths, and formulate queries involving these paths by means of a concise notation (functional join) The third approach attempts to solve the query inference problem, which consists in deducting from a sentence of a query language an 3 unambiguous interpretation of the query. For this purpose [11] and [19] introduced the universal relation, which is a single relation including all the relations in a given database, combined by means of natural joins. The universal relation relieves the user from the task of expliciting joins, but asks for requirements not always satisfied in practical ....

R. Fagin, A.O. Mendelzon and J.D. Ullman, "A simplified universal relation assumption and its properties", in ACM Trans. Database Syst., vol. 7, no. 3, pp. 343-360, 1982.

....matrix and the export schemas together represent the federated metadata needed for cooperative query processing. The ACM utilizes the notion of universal relation as the underlying concept. 2.1. 1 Federated Universal Relation Universal relation is both a concept and an implementation framework [5, 6, 8, 16, 18]. As a concept, it refers to a super relation that is comprised of all attributes in a database. In effect, universal relation creates an illusion to the user that there is only a single relation in the database and hides from the user the existing logical database structure. As an implementation ....

Ronald Fagin, Alberto O. Mendelzon, and Jeffrey D. Ullman. A Simplified Universal Relation Assumption and its Properties. ACM Trans on Database Systems, 7(3):343--360, September 1982.

....a collection that represents a base class. If they are not, we can artificially interpret the collection components as single attribute aggregates, or correspondingly, a singular aggregate as a one element collection. One proposed view of a relational database is the so called universal relation [7, 14]. It is defined as a join of all the relations in the database. If there is no join attribute in two relations, a cartesian product is applied. In our interface, it is also possible to view all objects as elements of a single (root) class. However, from type constructor point of view, the object ....

....AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAAAAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA Figure 3: A class hierarchy in a table. representation of the class hierarchy (cf. universal relation [7]) This is not adequate, because the screen is not utilized efficiently. Moreover, the total number of attributes may grow relatively large, causing extensive horizontal scrolling. The objective should be that an excessive number of null values (of type not applicable ) need not be shown on the ....

Fagin, R., Mendelzon, A.O. and Ullman, J.D.: "A Simplified Universal Relation Assumption and Its Properties", ACM Trans. Database Systems, Vol. 7, No. 3., 1982, pp. 343-360.

....envision many thousands of resource agents distributed over the Internet, dynamically coming and going, each claiming a coverage over part of this ontology. An assumption that underlies all the algorithms in this paper is that domain ontology may be expressed as a unique Universal Relation[15] 16][6][11] This is true for the example movie schema and this Universal Relation is: title movie show review title year type theater time city source eval 3 Query Analysis 3.1 Definitions and Assumptions Assume a set of relations R where R = R 1 ; Rm and R may be expressed as a Universal ....

R. Fagin and J.D. Ullman A. Mendelzon. A simplified universal relation assumption and its properties. Rj2900, IBM Research Labs, San jose, California, 1980.

....be modeled explicitly by connecting the two attributes in a dotted path. It is important to point out that the Distinct Meaning Name Assumption is not the same as the Universal Relation Scheme Assumption (URSA) which suggests that attribute names in a universal relational schema must be distinct [10]. The URSA is a very restrictive assumption which is formulated to allow semantic reasoning to be accomplished in a syntactic manner with the aid of classical data dependencies. Under the URSA, the semantic relationships between attribute names are often unclear; the DMNA on the other hand, is ....

....a given project can be captured. ffl Every attribute name in the schema now refers to distinct objects in the real world, with the exception of E# and M#. We provide for this exception 1 This Unique Path Assumption appears to be of the same flavor as the Relationship Uniqueness Assumption (URA) [10] which insists that there should only be one semantic meaning between a given set of attributes, so it means that cycles in an ER schema are not allowed under this assumption. Emp Dept Proj Affiliate Participate D# Workstation Assign 1 W# E# ISA Mgr Manage P# 1 m M# 1 m 1 ISA 1 Collaborate 1 ....

R. Fagin, A. Mendelson, and J. Ullman. A simplified universal relation assumption and its properties. ACM Trans. Database Syst., 7(3):343--360, 1982.

....particular relational database management systems. ffl Network, hierarchical, or object oriented database models. ffl Distributed databases. Basic references for relational databases include Codd (1970) Date (1986) Maier (1983) and Ullman (1982) More advanced references include Fagin (1977) Fagin, Mendelzon Ullman (1982), Beeri, Fagin, Maier Yannakakis (1983) and Beeri Kifer (1986a, b, 1987) Connections to probability theory are mentioned in Pearl (1988) Geiger Pearl (1988, 1990) Geiger, Paz Pearl (1991) Lauritzen Spiegelhalter (1988) and Thoma (1989) 2 Database Concepts and Probability ....

Fagin, R., Mendelzon, A. O. & Ullman, J. F. (1982). A simplified universal relation assumption and its properties. ACM Transactions on Database Systems 7, 343-360.

....where we have used abbreviation U for University, and appropriate letters for the other labels. Database schemes are often profitably represented as hypergraphs, whose nodes are the attributes (equivalently, OEM labels) and whose hyperedges are the relation schemes or sets of attributes; see Fagin, Mendelzon, and Ullman [1982], Ullman [1989] or (for an equivalent notation) Bernstein and Goodman [1981] For instance, the database scheme implied by Fig. 1.1 is shown in Fig. 1.2. Univ. Dept. Faculty Student Addr. Fig. 1.2. Hypergraph representation of university OEM objects. Maximizing the Connections Among Facts ....

....ordering. III. Gamma Acyclic Hypergraphs The class of fl acyclic hypergraphs is one of several kinds of acyclic hypergraphs studied by Fagin [1983] It is a special case of the more common class of acyclic hypergraph of Graham [1979] Yu and Ozsoyoglu [1979] Bernstein and Goodman [1981] or Fagin, Mendelzon, and Ullman [1982], which Fagin [1983] calls ff acyclic, Fagin [1983] gives several equivalent definitions of fl acyclicity. We shall only give here those definitions that are of use in our characterization of the hypergraphs for which a full disjunction can be computed by outerjoins in some order; those are ....

Fagin, R., A. O. Mendelzon, and J. D. Ullman [1982]. "A simplified universal relation assumption and its properties," ACM Trans. on Database Systems 7:3, pp. 343--360.

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R. Fagin, A. Mendelzon, and J. Ullman. A simplified universal relation assumption and its properties. ACM Transactions on Database Systems, 7, 1982.

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R. Fagin, A. Mendelzon, and J. Ullman. A simplified universal relation assumption and its properties. ACM Transactions on Database Systems, 7, 1982.

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R. Fagin, A.O. Mendelzon, and J.D. Ullman. A simplified universal relation assumption and its properties. ACM Transactions on Database Systems, 7(3):343--360, 1982.

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R. Fagin, A. Mendelzon, and J. Ullman. A simplified universal relation assumption and its properties. ACM Transactions on Database Systems, 7, 1982.

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R. Fagin, A. Mendelzon, and J. Ullman. A simplified universal relation assumption and its properties. ACM Transactions on Database Systems, 7, 1982.

No context found.

R. Fagin, A.O. Mendelzon, and J.D. Ullman. A simplifiedu niversal relation assu mption and its properties. ACM Transactions on Database Systems, 7(3):343--360, September 1982.

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R. Fagin, A. Mendelzon, and J. Ullman. A simplified universal relation assumption and its properties. ACM Transactions on Database Systems, 7, 1982.

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Fagin, R., Mendelzon, A. O., Ullmann, J. D. "A Simplified Universal Relation Assumption and its Properties", ACM TODS, Vol. 7, No. 3. 1982.

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