By Luca Cardelli (auth.), Richard Connor, Alberto Mendelzon (eds.)
This publication constitutes the completely refereed post-proceedings of the seventh foreign Workshop on Database Programming Languages, DBPL'99, held in Kinloch Rannoch, united kingdom in September 1999. The 17 revised complete papers offered including an invited paper have been rigorously reviewed and revised for inclusion within the ebook. The ebook provides topical sections on querying and question optmization; languages for rfile versions; endurance, parts and workflows; typing and querying semistructured facts; energetic and spatial databases; and unifying semistructured and conventional facts types.
Read or Download Research Issues in Structured and Semistructured Database Programming: 7th International Workshop on Database Programming Languages, DBPL’99 Kinloch Rannoch, UK, September 1–3,1999 Revised Papers PDF
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Extra resources for Research Issues in Structured and Semistructured Database Programming: 7th International Workshop on Database Programming Languages, DBPL’99 Kinloch Rannoch, UK, September 1–3,1999 Revised Papers
Sample text
In this paper we propose an approach which uni es and generalizes the approaches mentioned above. We apply the selection propagation" idea to certain data dependencies that are implicit in aggregation blocks. Propagation of SQL predicates MFPR90a, MFPR90b, MPR90, LMS94 is a special case of propagation of these dependencies. At the same time, propagating these dependencies R. Connor and A. ): DBPL’99, LNCS 1949, pp. 31-42, 2000. c Springer-Verlag Berlin Heidelberg 2000 32 Vasilis Aggelis and Stavros Cosmadakis can produce execution plans with alternative nesting structure, as in Day87, GW87, Kim82, Mur92, PHH92, YL94, HG94 .
The tuple n, p, hmax will be in the result of maxhours just in case the relation enrolled contains some tuple n, p, c and the relation timetable contains some tuple c, h . Notice that c, h are nondistinguished variables. The last line of the tableau expresses aggregation and grouping: it states that, for each xed n and p, hmax is the maximum possible value of h. A similar formulation of aggregation is described in Klug82 . A tableau corresponding to a subquery contains special non-local variables they are local to the tableau obtained from the enclosing query block.
For a relation 2 , we denote its type by tp . Expressions of the language over a xed relational schema are shown in Figure 1. We adopt the convention of omitting the explicit type superscripts in these expressions whenever they can be inferred from the context. We brie y explain the semantics here. , n are free variables of . Expressions f 1 j Pf 1 j that 2 2 g bind the variable furthermore, is not allowed to be free in 2 for this expression to be well-formed . For each xed schema and an expression 1 n , the value of induction on the structure of and with re 1 is de ned by n spect to a -database and a substitution 1 := 1 n := n that assigns to each variable i a value i of the appropriate type.