We address the problem of tight XML schemas and propose regular tree automata to model XML data. We show that the tree automata model is more powerful that the XML DTDs and is closed under main algebraic operations. We introduce the XML query algebra based the tree automata model, and discuss the query optimization and query pruning techniques. Finally, we show the conversion of tree automata schema into XML DTDs.

We propose a set of operations for inquiring about the properties of individual objects and classes in an object-oriented database. The operations are closely related to the constructs introduced by our formalisation of the object-oriented data model, through which we unify the representation of the intensional and the extensional portions of the object-oriented database. As a consequence, they provide a uniform access to the extensional and the intensional parts of the objectoriented database. The proposed operations are used for inquiring about the associations among individual objects, the relationships between individual objects and class objects, and the relationships among the class objects themselves. We show that if they are integrated into an object algebra, they can serve for querying the intensional portion of the database, and for using the relationships between individual objects and the conceptual schema in conventional queries. 1 Introduction In an object-oriented (OO) ...

In this thesis, we address the problems of the design of an object algebra whose operations are intended to form the basis of OVAL, a functional query language for objects. The proposed algebra is closely related to the object-oriented database model. The algebra and the corresponding functional language are designed to be suitable for integration with an object-oriented database programming language. The main contributions of the work are: (i) the definition of the object algebra, (ii) the design of a functional operation for querying nested components of complex objects, (iii) the definition of a set of operations for querying database schema, and finally, (iv) the design of a procedure for static type checking of OVAL queries. In order to provide the basis for the definition of the object algebra operations, we describe the object-oriented model in a formal manner. The proposed object-oriented model formalization unifies the schema and the instances of the database. Consequently, th...

Syntax of Object Comprehensions Es ::= E j E , Es E ::= E union E j E differ E j [ Xs --- E ] j E and E j E or E j not E j E hasClass E j E hasClass E with E j Y E ! Y E j E / E j E . E j I( Es ) j I j K j f Es g j f E : : : E g j E . [ E ] j A E j ( E ) Xs ::= j X j X ; Xs X ::= D j L j E D ::= I / E L ::= I as E Y ::= j some j atleast E j just E j atmost E j every A ::= size ::= set j bag j list ! ::= = j = j ? j ?= j ! j != j == j == / ::= * j / j + j - B Abstract Syntax of Function Arguments F ::= I . E j F ffi F Es ::= E j E, Es E ::= E . E j I( Es ) j E ff E j E ! E j E / E j I j K j ( E ) j Q ff ::= j j : ! ::= = j = j ? j ?= j ! j != / ::= * j / j + j - 22 References ...

The main motivation for the development of a query algebra of complex objects QAL is the study of the operations needed to query the structural aspects of object-oriented databases which are due to the advantages of the object-oriented database model over conventional relational and functional database models. The basic operations of the QAL query algebra evolved from relational algebras and the FQL family of functional query languages by re#ning their operations for the manipulation of objects. In order to support the features speci#c to object-oriented data models, QAL o#ers: #i# a set of operations which provide the means for querying conceptual schemata, and #ii# an operation which provides a simple and e#cientway of querying nested components of complex objects. We show through a case-study consisting of a comprehensive set of examples how these operations can be employed to express a class of queries speci#c to object-oriented databases. Index terms: Database algebras, ...

. This paper describes the database algebra QAL which serves as the logical algebra in the query execution system of the Distributed Object Kernel #25#. QAL is based on the concepts of the early functional query languages. It provides a simple functional semantics of the language and the means to express complex queries in a step-by-step manner. The operations of QAL are designed to allow simple and e#cient manipulation of objects having rich classi#cation structure, complex hierarchical or network structure. The expressivepower of QAL is presented through a case-study consisting of a comprehensive set of examples of queries which manipulate complex objects. 1 Introduction Database management systems are employed for storing data in many novel computer applications ranging from computer aided design, process control and computer integrated manufacturing to software engineering, multimedia and Internet applications. Novel demands for the representation and manipulation of th...

In this paper we present the consequences of unifying the representation of the schema and the instance levels of an object-oriented (OO) database to the formal representation of OO database model. The uniform representation of the schema and the instance levels of OO databases is achieved, as in the frame-based knowledge representation languages [13], by representing them using a uniform set of modelling constructs. We show that, using such an approach, the structural part of the OO database model can be described in a clear manner providing the simple means for the description of the main constructs of the structural model and the relationships among them. Further, we study the consequences of releasing the boundary between the schema and the instance levels of an OO database by allowing the definition of objects which include data from both levels. We show that few changes are needed in order to augment the previously presented formal definition of the structural part o...

We propose the set of operations for querying the conceptual schema of an objectoriented database. The operations form the basis of an algebra for objects called OVAL. They are defined using the constructs introduced for our formalization of the object-oriented database model. The operations allow a user to query: (i) associations among individual objects, (ii) relationships between individual objects and class objects, and (iii) relationships among class objects themselves. 1 Introduction Object-oriented database model provides a rich set of modeling constructs that make the conceptual schema of an object-oriented database more expressive than relational schemas. We observe that, comparing a relational database to an object-oriented one, some information about the modeling environment has been moved from the data part to the schema part of the database. Hence, some aspects of the modeling environment can be, using an objectoriented database model, represented and stored in a databas...

Nested loop execution of object-oriented queries retains the promise of maintaining the full generality of the object paradigm, independent of the specifics of any single object model. Thus, from this starting point we have developed an object-oriented query optimizer and execution engine. The methods, developed to date for only acyclic queries, augment nested loops structures with a simple marking mechanism such that unnecessary loop iterations are not repeated. In the case of acyclic queries, the executions are asymptotically optimal. In contrast to optimal query methods based on semijoin reductions our method involves no preprocessing step and thus avoids the extra I/O associated with semijoins and prevents the formal benefits of semijoin reduction from appearing as a practical improvement. Empirical results comparing our query environment with a commercially available product demonstrate significant performance improvement. 1 Introduction We develop a technique for the optimizatio...

While much recent research has focussed on extending databases beyond the traditional relational model, relatively little has been done to develop database tools for querying data organized in (multidimensional) arrays. The scientific computing community has made little use of available database technology. Instead, multidimensional scientific data is typically stored in local files conforming to various data exchange formats and queried via specialized access libraries tied in to general purpose programming languages. To allow such data to be queried using known database techniques, we design and implement a query language for multidimensional arrays. Our main design decision is to treat arrays as functions from index sets to values rather than as collection types. This leads to clean syntax and semantics as well as simple but powerful optimization rules. We present a calculus for arrays that extends standard calculi for complex objects. We derive a higher-level comprehension style ...