Principles of database and knowledge-base systems, Vol. I
Principles of database and knowledge-base systems, Vol. I
Logic-based approach to semantic query optimization
ACM Transactions on Database Systems (TODS)
Clique partitions, graph compression and speeding-up algorithms
STOC '91 Proceedings of the twenty-third annual ACM symposium on Theory of computing
PODS '91 Proceedings of the tenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Answering queries using views (extended abstract)
PODS '95 Proceedings of the fourteenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Journal of Intelligent Information Systems
Computers and Intractability: A Guide to the Theory of NP-Completeness
Computers and Intractability: A Guide to the Theory of NP-Completeness
On the Multiple-Query Optimization Problem
IEEE Transactions on Knowledge and Data Engineering
Security Constraint Processing in a Multilevel Secure Distributed Database Management System
IEEE Transactions on Knowledge and Data Engineering
Overview of Dynamic Query Evaluationin Intensional Query Optimization
DOOD '97 Proceedings of the 5th International Conference on Deductive and Object-Oriented Databases
Semantic Query Reformulation in Deductive Databases
Proceedings of the Seventh International Conference on Data Engineering
ICDE '95 Proceedings of the Eleventh International Conference on Data Engineering
Semantic Data Caching and Replacement
VLDB '96 Proceedings of the 22th International Conference on Very Large Data Bases
Semantic Query Optimization for Bottom-Up Evaluation
ISMIS '96 Proceedings of the 9th International Symposium on Foundations of Intelligent Systems
Answering queries using views: A survey
The VLDB Journal — The International Journal on Very Large Data Bases
An architecture and implementation for a cooperative database system
An architecture and implementation for a cooperative database system
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We explore a new form of view rewrite called view disassembly. The objective is to rewrite views in order to ''remove'' certain sub-views (or unfoldings) of the view. This becomes pertinent for complex views which may be defined over other views and which may involve union. Such complex views arise necessarily in environments such as data warehousing and mediation over heterogeneous databases. View disassembly can be used for view and query optimization, preserving data security, making use of cached queries and materialized views, and view maintenance. We provide computational complexity results of view disassembly. One question is whether the unfoldings to be removed effectively cover the view, meaning that the disassembled view is effectively the empty view, evaluating to the empty table. We illustrate the complexity to determine when a collection of unfoldings cover the view definition. The problem is NP-hard with respect to the number of unfoldings to remove, but not with respect to the size (complexity) of the view definition. We next consider rewrites optimal in the size of the rewritten (disassembled) view. We prove that this task is NP-hard for a special class of views, but this time NP-hard in a worse way: it is NP-hard this time with respect to the size of the view definition in addition to the number of unfoldings to be removed. In general, we suspect the problem is computationally even harder, and we show that the general problem is in @P"2^p. However, we provide good news too. We identify a pertinent class of unfoldings for which the removal of such unfoldings always results in a simpler disassembled view than the original view itself. We also develop an algorithm that finds rewrites equivalent to the disassembled view which are, in a sense, locally optimal. The algorithm establishes a cover completion by finding a (minimal) collection of unfoldings of the view that, along with the unfoldings to be removed, covers the original view. This approach is effectively tractable, unlike the search for globally, or absolutely, optimal rewrites. Furthermore, we show that these cover-completion rewrites are preferable to absolutely optimal rewrites in many ways.