H.-J. Schek and M. H. Scholl. The relational model with relation-valued attributes. Information Systems, 11(2):137--147, 1986.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....involving transitive relationships. The poor capability of the conventional relational model in modeling and processing complex objects in many applications, including information retrieval (IR) has led many researchers to study the NF 2 relational model, i.e. non first normal form relations [8], object oriented da tabases, deductive databases and deductive object oriented databases (e.g. 9, 10, 11] Bib liographic data are naturally modeled as NF 2 relations [12, 13] Moreover, some terminologi cal network structures, e.g. thesauri and classifications, and citation networks are ....

Sheck, H.-J. & Scholl, M.H. The relational model with relation-valued attributes. In- formation Systems, 11(2), 1986, 137-147.

....i.e. setorientation was mostly out of their scope. The database was queried in a navigational manner along the references defined between the database objects (e.g. path expressions in OPAL [33] By now a lot of research focuses on full fledged query languages for object oriented database models [22, 44]. Seen from a more general point of view the upcoming object oriented query languages exploit facilities to query along predefined relationships (in [6] called functional join) as well as to use traditional value based relational join capabilities. The functional join facility resembles the ....

H.-J. Schek and M.H. Scholl,, The Relational Model with Relation-Valued Attributes, in: Information Systems 2 (1986) 137-147.

....1. Introduction Object oriented data models [4, 5, 6, 7, 17, 27] attempt to overcome some of the deficiencies of value oriented data models [9, 16, 25] The predominant value oriented data model has been the relational model [9] which is limited to flat relational structures. Nested relations [19, 21, 26] extend the applicability of the relational model by allowing hierarchical objects to be modelled directly. In the relational model, both conventional and nested, objects are identified by the values of their attributes, whereas in object oriented data models object identity is independent of ....

....Jill has been logically identified as a sub object of O. We now define an attribute and its corresponding domain to be either atomic or the result of nesting a set of already defined attributes. We note that this is analogous to the definition of an attribute in a nested relation scheme [19, 21, 26]. Definition 2.1. An attribute and its corresponding domain are defined recursively as follows : 1) The atomic attributes A 1 , A p , are attributes with associated domains DOM(A 1 ) DOM(A p ) respectively. We assume that each domain DOM(A i ) has a bottom [24] element A i ....

SCHEK H.-J., AND SCHOLL M. H. 1986. The relational model with relation-valued attributes. Information Systems 11, pp. 137-147.

....instance approach [3, 13, 15, 24, 26] In the weak instance approach to the UR model, the representative instance (RI) 24, 26, 27] becomes the underlying data structure of the UR model, which is suitable for storing all the data in the database in a single relation. The nested relational model [1, 17, 28, 34] was developed in order to extend the applicability of the flat relational model to more complex non business applications. Nested relations do not necessarily conform to the first normal form assumption of the flat relational model [8] thus allowing hierarchically structured complex objects to ....

....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 ....

[Article contains additional citation context not shown here]

H.-J. SCHEK AND M.H. SCHOLL, The relational model with relation-valued attributes, Inf. Systems 11, No. 2 (1986), 137-147.

....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]

H.-J. Schek and M.H. Scholl, The relational model with relation-valued attributes, Inf. Syst. 11 (1986) 137-147.

....invalidating the underlying relational model As mentioned earlier, the relational model has a mathematically rigorous definition to guarantee predictable, correct results on any database systems that faithfully implements the model. Detailed examination [AB84] FT83] KK89] Mak77] SP82] SS86] has been made of the relational model with the 1NF constraint removed. The analysis has proven that the resulting model is equally robust. In other words, removing the 1NF constraint will not cause a relational database to produce invalid or inconsistent results as long as the database conforms ....

H. Schek and M. Scholl. The relational model with relation-valued attributes. Information Systems, 11(2):137--147, 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 ....

....aspects, is extended. The language as it stands now is just a theoretical realization of the standard nested algebra, and does not allow an effective manipulation of nested relations. In order to allow for this, operations of extended nested algebras, such as nested application of projection [17] and more general, flexible selection conditions have to be incorporated. Other important aspects from a more practical point of view, such as aggregate functions and arithmetic, should not cause too much problems to be integrated in NSQL. A more fundamental issue for further research, as ....

H.-J. Scheck, M. Scholl: "The relational model with relation-valued attributes ", Information systems 11,2, pp. 137--147, 1986.

....In the quest for extending the abilities of relational database systems without losing the advantages of such systems, the Address: University of Antwerp (UIA) Dept. Math. Comp. Science, Universiteitsplein 1, B 2610 Antwerp, Belgium. E mail: vdbuss ccu.uia.ac.be. 1 nested relational model [SS86, TF86] was a particularly elegant step forward. Roughly, the components of the tuples in a nested relation need not be unstructured values, but can be (nested) relations in turn. Relational query languages can be extended to work on nested relational databases. But, due to the richer data ....

H.-J. Schek and M.H. Scholl. The relational model with relationvalued attributes. Information Systems, 11(2):137--147, 1986.

....conditions; however, Verso selections work only on the top level. Actually, the focus of [Bid87] is more on succinctly expressing relational tableau queries through Verso super selection; this is possible since Verso databases correspond to universal relation databases. In [AB88, BCD89, BK90, SS86] among others) a more algebraic approach is taken in defining powerful selection operations, by allowing other algebra operations to appear in selection conditions, as in select [ C] Z) D] W ) The optimization problem may then be attacked by finding algebraic equivalences, stating ....

....can be used complementary. And conversely, the restricted class of selections we considered in Sections 4 and 5 is able to capture most selection operations usually encountered in the literature (and many others too) A typical representative of these are the extended selections defined in [SS86] Their corresponding conditions are formulas built from comparisons based on = 2 (including dynamic constants ) negation, logical connectives, and a limited form of existential quantification (due to the recursive use of projection and selection within the conditions) It can be shown ....

H.-J. Schek and M.H. Scholl. The relational model with relation-valued attributes. Information Systems, 11(2):137--147, 1986.

....: f(x n ) that is, it extends f to sets. This function is well defined. Using ext together with j, projections and record formation, conditional and the equality test gives us precisely the nested relational algebra [3] but the presentation is nicer than the standard ones, such as in [32]. This approach to the language design has proved extremely fruitful and allowed to solve some open problems (e.g. 24] and develop languages for other collections (e.g. 22, 23] In order to apply it to the approximation constructs, we first need formal models of those, and then the ....

H.-J. Schek and M. Scholl, The relational model with relation-valued attributes, Inf. Syst. 11 (1986), 137--147.

....key, URL) turning trees into some type of well formed graph. Moreover, unlike unstructured Web pages, they will all come with a schema and will map into some type of XML document [26 37] if needed. For our purposes we found the nested relational data model (non first normal form, NF 2 model [17]) very useful. First of all it is properly defined. Secondly, it has an attractive visualization either as tree or nested table. Thirdly, it permits intuitive navigation as shown below. Finally, it can be mapped in an intuitive, simple way into XML structures, as shown by procedure fingertodom( ....

H.-J.Schek and M.H.Scholl. The Relational Model with Relation-Valued Attributes, Information Systems, 11(2), 1986, pp. 137 -- 147.

....The resulting equivalent expression is more ecient than the original one. 7 Conclusion The nested relational model provides a better way of representing complex objects than the traditional relational model, and allows users to describe their concepts of real world data objects more easily [1, 3, 21] However, the optimization of queries is di erent from that in the 1NF relational model. In this paper we have investigated some algebraic properties of nested relational operators which are useful for query optimization in the nested relational model. We have discussed the interactions of ....

H. Schek and M. Scholl. The Relational Model with Relation-Valued Attributes. Information Systems, 11(2), 1986, pp. 137-147.

....possibly containing other sets, the databases are no longer in the first normal form. Therefore, we have to deal with nested relations, or complex objects. The language we describe contains the nested relational algebra as a sublanguage. The standard presentations of the nested relational algebra [7, 24, 25] have a cumbersome syntax. Therefore, we have decided to follow the approach of [3] which gives a very clean and simple language that has precisely the expressive power of the nested relational algebra. The relational language introduced in [3] was based on earlier languages for lists [27, 28] ....

H.-J. Schek and M. Scholl, The relational model with relation-valued attributes, Inform. Systems 11 (1986), 137--147.

....any subset of the descriptive attributes of . The geometric projection of on denoted S y z dBo when there is no ambiguity, is defined as: do e X [4[ B d F # d x y z do [ 4 applies f to some attribute of each tuple of F # is the N1NF grouping operation [BRS82, AB86, SS86] on and y z r 3 r 3 is the (geometric) sum agregate function where is (overloaded with) the set union over . Theorem 1: is closed under geometric projection and geometric join. Proof (sketch) one easily shows [Rig95] that x y z ,d dBo and that there is a bijection ....

H. J. Schek and M. H. Scholl. The Relational Model with Relation-Valued Attributes. Information Systems, 1986.

No context found.

H.-J. Schek and M. H. Scholl. The relational model with relation-valued attributes. Information Systems, 11(2):137--147, 1986.

No context found.

H.-J. Schek and M. H. Scholl. The relational model with relation-valued attributes. Information Systems, 11(2):137--147, 1986.

No context found.

H.-J. Schek and M. H. Scholl. The relational model with relation-valued attributes. Information Systems, 11(2):137--147, 1986.

No context found.

H.-J. Schek, M. H. Scholl, The relational model with relation-valued attributes, Information Systems 11, No. 2 (1986), 137--147.

No context found.

H.J. Schek and M.H. Scholl. The relational model with relation-valued attributes. Information Systems, 11(2):137--147, 1986.

No context found.

H.J. Schek and M.H. Scholl. The relational model with relation-valued attributes. Information Systems, 11(2):137--147, 1986.

No context found.

H.J. Schek and M.H. Scholl. The relational model with relation-valued attributes. Information Systems, 11(2):137--147, 1986.

No context found.

H.J. Schek and M.H. Scholl. The relational model with relation-valued attributes. Information Systems, 11(2):137--147, 1986.

No context found.

H.-J. Schek and M. H. Scholl. The relational model with relation-valued attributes. Information Systems, 11(2):137--147, 1986.

No context found.

H.J. Schek and M.H. Scholl. The relational model with relation-valued attributes. Information Systems, 11(2):137--147, 1986.

No context found.

H.-J. Schek and M. H. Scholl. The relational model with relation-valued attributes. Information Systems, 11(2):137-147, 1986.

First 50 documents  Next 50

Online articles have much greater impact   More about CiteSeer.IST   Add search form to your site   Submit documents   Feedback  

CiteSeer.IST - Copyright Penn State and NEC