Browsing by Subject "Query language"

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Open Access
Object-oriented query language facilitating construction of new objects
(Elsevier, 1993) Alhajj, R.; Arkun, M. E.
In object-oriented database systems, messages can be used to manipulate the database; however, a query language is still a required component of any kind of database system. In the paper, we describe a query language for object-oriented databases where both objects as well as behaviour defined in them are handled. Not only existing objects are manipulated; the introduction of new relationships and new objects constructed out of existing ones is also facilitated. The operations supported in the described query language subsumes those of the relational algebra aiming at a more powerful query language than the relational algebra. Among the additional operators, there is an operator that handles the application of an aggregate function on objects in an operand while still having the result possessing the characteristics of an operand. The result of a query as well as the operands are considered to have a pair of sets, a set of objects and a set of message expressions; where a message expression is a sequence of messages. A message expression handles both stored and derived values and hence provides a full computational power without having an embedded query language with impedance mismatch. Therefore the closure property is maintained by having the result of a query possessing the characteristics of an operand. Furthermore, we define a set of objects and derive a set of message expressions for every class; hence any class can be an operand. Moreover, the result of a query has the characteristics of a class and its superclass/subclass relationships with the operands are established to make it persistent. © 1993.
Open Access
An object-oriented structured query language and its translation to a formal algebra
(1997) Gür, Ali Gürhan
A declarative query capability has been accepted as a fundamental feature of any database management system. This thesis proposes an extension of the standard query language SQL, SQL/OO, designed for querying object-oriented databases. It has additional constructs to deal with the rich data model introduced by object-orientation. SQL/OO rests on a formal object-oriented query algebra that is highly expressive and open to optimization. Formal definitions of syntax and semantics are presented. The mapping of SQL/OO queries into object algebra is provided by a syntax-directed translation scheme. A prototype system that evaluates SQL/OO queries is designed. The system starts with a translator that translates an SQL/OO query into an equivalent object algebra expression. This algebra expression is parsed and an Object Algebra Tree (OAT) is generated which will be used as the internal representation. OAT Trees can be used as the input and output of a query optimizer module. The result of the query will be evaluated by traversing the tree and evaluating each node using proper functions that execute object algebra operations. A survey of existing object-oriented query languages in the literature is also provided. Their characteristics are identified, compared and contrasted, in order to present the necessary background.