Optimization of Object Query Languages
نویسنده
چکیده
Transformation of nested SQL queries into join queries is advantageous because a nestedSQL query can be looked upon as a nested-loop join, which is just one of the several joinimplementations that may be available in a relational DBMS. In join queries, dangling(unmatched) operand tuples are lost, which causes a problem in transforming nestedqueries having the aggregate function COUNT between query blocks–a problem thathas become well-known as the COUNT bug. In the relational context, the outerjoin hasbeen employed to solve the COUNT bug. In complex object models supporting an SQL-like query language, transformation of nested queries into join queries is an importantoptimization issue as well. The COUNT bug turns out to be a special case of a generalproblem being revealed in a complex object model. To solve the more general problem,we introduce the nestjoin operator, which is a generalization of the outerjoin for complexobjects.
منابع مشابه
An Object Based Algebra for Parallel Query Processing and Optimization
The Tarski algebra provides an algebraic foundation for object-based query languages. This is demonstrated by showing how queries expressed in a graph-oriented query language (based on the functional data model) can be translated into the Tarski algebra. The graphical representation of queries in combination with the Tarski algebra is a convenient mechanism to study optimization in the context ...
متن کاملQuery Optimization in Object Oriented Databases through Detecting Independent Subqueries
Query optimization is the refining process in database administration and it helps to bring down speed of execution. Some object-oriented languages allows to express queries explicitly in the code, which are optimized using the query optimization techniques from the database domain. With respect to this, a formalized object query language (OQL) has been developed that performs optimization of q...
متن کاملImplementation of Optimization in Object-Oriented Queries
Query optimization techniques are dependent upon the query model and language. The query model, in turn, is based on the data (or object) model since it defines the access primitives which are used by the query model. These primitives determine the power of the query model. Object-oriented languages allow expressing queries explicitly in the code, which are optimized using the query optimizatio...
متن کاملQuery Optimization Techniques Exploiting Class Hierarchies
Since the introduction of object base management systems (OBMS), many query optimization techniques tailored for object query languages have been proposed. They adapt known optimization techniques to the OBMS context, exploit special object-oriented features, or give solutions to problems speciic to querying objects. Nonetheless, one of the most prominent features of object models | namely clas...
متن کاملVisualMOQL: The DISIMA Visual Query Language
Multimedia data are now available to a variety of users ranging from naive to sophisticated. To make querying easy, visual query languages have been proposed. Most of these languages have a low expressive power and have their own query processors. Efforts have been made to design query languages with proper semantics to facilitate query optimization and processing in existing database systems. ...
متن کاملAlgebraic Foundation and Optimization for Object Based Query Languages
We introduce the Tarski algebra aa an algebraic foundation for object baaed query languages. While maintaining physical data independence, ihe Tarski algebra is shown to be both simple and powerful enough to ezpress all reasonable queries. We show how queries ezpressed in a graph-oriented query language (baaed on the functional data model) can be translated into the Tarski algebra. The graphica...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
دوره شماره
صفحات -
تاریخ انتشار 1995