Design and Query Strategies to Hypermedia Applications

In this paper we propose an object-oriented model for designing hypermedia applications. As the object-oriented paradigm allows complex and user-defined types, nonconventional and nonatomic attributes, we can take advantage of these capabilities, not only for information modelling, but also for providing alternative ways for accessing information.A query language is then presented; it is based on an Object-Oriented Database System query language. It combines features of object-oriented databases queries and primitives for hypermedia navigation. The language offers the possibility of querying both the application-domain information, and allowing the designers to obtain information about the schema of the application.We present some examples of the use of the object-oriented model and the query language.     

Multi-paradigm query interface to an object-oriented database

The object-oriented paradigm has a number of widely recognised strengths when applied to data management, but the increased complexity of actual systems compared with their relational predecessors often means that such databases are less readily accessible to nonprogrammers than relational systems. A number of proposals have been made for textual, form-based and graph-based query interfaces to object-oriented databases, but it is clear that a single approach cannot be considered to be the best, given the wide range of potential user groups, application domains and tasks. The paper presents a query interface to an object-oriented database which supports alternative user-level query paradigms in a fully integrated environment, thereby enabling different categories of user to select a preferred interface paradigm from a list of options. Furthermore, the interface enables users to examine queries written in one query interface using any of the other interface paradigms, which is useful for sharing queries in the multi-paradigm context, and for helping users familiar with one approach to learn another. The system has been prototyped using the ADAM object-oriented database system, and an experimental comparison of different interaction modes has been conducted.     

Knowledge object modeling

Knowledge objects are an integration of the object-oriented paradigm with logic rules. The proper integration provides a flexible and powerful environment, as rule-based components provide facilities for deductive retrieval and pattern matching, and object-oriented components provide a clear intuitive structure for programs in the form of class hierarchies. Based on the knowledge object concept, this paper presents a factor-centered representation language, Factor++, which models logic rules into the object-oriented paradigm, and a scheduling system, Schedular, using the Factor++ framework The construction of Schedular demonstrates that by using an object-oriented representation of knowledge objects, users can be given explicit control of the object hierarchy to customize the system to their particular needs, which includes letting users select among scheduling and other methods. In Schedular, rules are designed as derivation rules and constraint rules. The purpose of rules is either to restrict object structure and behavior, or to infer new data from the existing data. Rules are arranged in positions so that object methods are automatically firing up if environment changes are detected by these rules     

RELOOP, an algebra based query language for an object-oriented database system

In most object-oriented databases, as opposed to value-oriented databases, data are accessed by a programming language instead of a declarative query language. End users do not have a simple tool to perform their queries. This paper is concerned with the definition of an SQL-like query language on top of the O₂ object-oriented database system. We study the influence of the object-oriented paradigm on a query language, describe our language through examples, define its semantics by means of an algebra and sketch the compilation of RELOOP in one of the languages supported by the O₂ system.     

Design and Implementation of the ROL Deductive Object-Oriented Database System

ROL is a deductive object-oriented database system that has been implemented at the University of Regina. It provides a uniform rule-based declarative language for defining, manipulating and querying databases, which integrates important features of both deductive databases and object-oriented databases. It supports object identity, complex objects, classes, class hierarchies, multiple inheritance with overriding and blocking, and schema definition. It also supports structured values such as functor objects and sets, treating them as first class citizens, and providing powerful mechanisms for representing both partial and complete information about sets. This paper describes its design and implementation. An important novel feature of the implementation is that it combines top-down and bottom-up evaluation strategies and automatically selects a strategy based on the nature of the query and data in the database.     

一种面向对象DBMS的直观对象查询语言

文章论述了一种面向对象的数据库管理系统的直观对象查询语言。这种基于图形的查询语言可支持图表式查询语言的定义和说明,因此这种语言既有基于文本的结构查询语言的表达能力,也具有基于图形查询语言的直观性。     

A Hybrid Fragmentation Approach for Distributed Deductive Database Systems

Fragmentation of base relations in distributed database management systems increases the level of concurrency and therefore system throughput for query processing. Algorithms for horizontal and vertical fragmentation of relations in relational, object-oriented and deductive databases exist; however, hybrid fragmentation techniques based on variable bindings appearing in user queries and query-access-rule dependency are lacking for deductive database systems. In this paper, we propose a hybrid fragmentation approach for distributed deductive database systems. Our approach first considers the horizontal partition of base relations according to the bindings imposed on user queries, and then generates vertical fragments of the horizontally partitioned relations and clusters rules using affinity of attributes and access frequency of queries and rules. The proposed fragmentation technique facilitates the design of distributed deductive database systems. Received 4 August 1999 / Revised 30 March 2000 / Accepted in revised form 6 October 2000     

DOOL程序语义等价转换为Datalog 程序的转换规则

演绎对象数据库(DOOD)是演绎数据库与面向对象数据库两者优点相结合的产物。笔者设计实现了一个演绎对象数据库系统原型SD-DOOD,它是基于演绎数据库系统SD-DDBS的。然而,它使用的是演绎对象库语言DOOL,而演绎数据库语言是基于Datalog的,因此该文提出了应用一些转换规则来将DOOL程序转换为Datalog,通过规则转换,能求出DOOL程序的最小不动点(即程序值),从而使得系统的查询操作全都由SD-DDBS最终得出结果。文中详细介绍了转换规则的具体内容。     

QBD*: a graphical query language with recursion

A system to query databases using diagrams as a standard user interface is proposed. The system, called Query by Diagram* (QBD*), makes use of a conceptual data model, a query language on this model, and a graphical user interface. The conceptual model is the entity-relationship model. The query language, whose expressive power allows recursive queries, supports visual interaction. The main characteristics of the interface are ease of use and the availability of a rich set of primitives for schema selection and query formulation. The expressive power of QBD* and G⁺, which are the only languages allowing recursive queries to be expressed graphically are compared     

PSE: An Object-Oriented Representation for Modeling and Managing Part-of Relationships

Part-of relationships are needed to model structures of composite objects. Especially, composite objects, known as physical assemblies, are very popular in several applications. The existing object-oriented representations of physical assemblies and query languages based on them have several disadvantages. For example, they suppose that the user knows the structure of a physical assembly completely. This is not a realistic requirement in those cases where a physical assembly consists of a huge number of parts. Likewise the user has in them to control traversals of physical assemblies, i.e. they have a low degree of declarativity. Further, they do not support intensional and combined extensional-intensional queries which would be necessary in an advanced manipulation of physical assemblies. We develop the PSE (Part-of Structure Element) representation for removing the above disadvantages. The PSE representation is a set theoretical and constructor-oriented representation for physical assemblies and it can be used in the implementation based on both the object-oriented and deductive object-oriented database (DOOD) paradigms.     

VISIONARY: a Viewpoint-based Visual Language for Querying Relational Databases

The adoption of a visual interface can simplify the query formulation process in DBMSs by enabling naive users to interact with a friendly environment. In this work, we propose a visual query language based on a diagrammatic paradigm, used for both data and query representation. The external data model is called vision and is made up of the visual primitives of concept and association. The external query model is based on the definition of a viewpoint, which is a perspective for accessing data defined dynamically by selecting a concept of primary interest. Internally, the data model is relational and the query language is SQL. An intermediate graph-based model ensures consistent mapping between the visual and the relational worlds. Our language has been implemented within a tool which can be mounted on top of any relational DBMS supporting ODBC. The system has been tested with naive users; the results of the experiment are reported and compared with those obtained with other visual languages.     

Reasoning about equations and functional dependencies on complexobjects

Virtually all semantic or object-oriented data models assume that objects have an identity separate from any of their parts, and allow users to define complex object types in which part values may be any other objects. This often results in a choice of query language in which a user can express navigating from one object to another by following a property value path. We consider a constraint language in which one may express equations and functional dependencies over complex object types. The language is novel in the sense that component attributes of individual constraints may correspond to property paths. The kind of equations we consider are also important, because they are a natural abstraction of the class of conjunctive queries for query languages that support property value navigation. In our introductory comments, we give an example of such a query and outline two applications of the constraint theory to problems relating to a choice of access plan for the query. We present a sound and complete axiomatization of the constraint language for the case in which interpretations are permitted to be infinite, where interpretations themselves correspond to a form of directed labeled graph. Although the implication problem for our form of equational constraint alone over arbitrary schema is undecidable, we present decision procedures for the implication problem for both kinds of constraints when the problem schema satisfies a stratification condition, and when all input functional dependencies are keys     

ES-Kit: An object-oriented distributed system

This paper describes the design, implementation, and performance of ES-Kit, a distributed object-oriented system being developed by the Experimental Systems Project at the Microelectronics and Computer Technology Corporation. The operating system consists of a kernel and a set of Public Service Objects which dynamically extend the functionality of the kernel by providing several traditional operating system services when required by application objects. Applications for the ES-Kit environment are written in GNU C++ and do not require additional language primitives for distributed execution. Initial performance results from a representative set of applications indicate that the object-oriented paradigm provides a powerful solution to distributed programming.     

Query language feature analysis by usability

Over the last decade many database management systems have been developed with one or more query languages for user manipulation and modification of data. This paper presents the results of a comparative analysis performed on eighteen query languages. The purpose of this analysis is to identify and categorize the features which influence the usability of the language. To this end, seven broad categories are detailed: data models, language functions, expression complexity, language format, environment, intended user expertise and interface facilities. These categories are described with examples from the languages. The framework this categorization begins to develop may be useful to perspective users as well as new language designers.     

一个演绎对象数据库SD-DOOD的设计与实现

通过探寻面向对象数据库与知识库技术相结合的途径，研究演绎对象数据库系统实现的关键技术。以基于演绎数据库系统SD-DDBS，设计实现了一个演绎对象数据库系统原型SD-DOOD。系统支持类、类层次、对象、属性、方法、继承和封装等面向对象数据库系统的核心概念，支持演绎对象等演绎数据库的概念，提供了图形用户接口(GUI)，便于用户进行创建、查询等操作。     

M3Set — A language for handling of distributed and persistent sets of objects

We claim that distributed object-oriented systems must provide a higher level of abstraction to their users, than usually provided. Especially, it is necessary to provide application-oriented, intelligent aggregates of objects with transparent distribution of their elements. Beside that, it seems to be not only reasonable, but also relatively easy to connect persistence with distribution. A system, offering distributed and persistent polymorphic sets of objects, on the level of a clean, type safe programming language is introduced. The user of such a system gets distribution and persistence in the same “natural” way, as users of traditional systems get volatile arrays of numbers or classes of objects.     

G-Log: a graph-based query language

We introduce G-Log, a declarative query language based on graphs, which combines the expressive power of logic, the modeling power of complex objects with identity and the representation power of graphs. G-Log is a nondeterministic complete query language, and thus allows the expression of a large variety of queries. We compare G-Log to well-known deductive database languages, and find that it is the only nondeterministic and computationally complete language that does not suffer from the copy-elimination problem. G-Log may be used in a totally declarative way, as well as in a “more procedural” way. Thus, it provides an intuitive, flexible graph-based formalism for nonexpert database users     

Approaches to deductive object-oriented databases

The paper is concerned with the problem of combining deductive and object-oriented features to produce a deductive object-oriented database system which is comparable to those currently available under the relational view of data modelling not only in its functionality but also in the techniques employed in its construction and use. Under this assumption, the kinds of issues that have to be tackled for a similar research strategy to produce comparable results are highlighted. The authors motivate their terms of comparison, characterize three broad approaches to deductive object-oriented databases and introduce the notion of language convergence to help in the characterization of some shortcomings that have been perceived in them. Three proposals that have come to light in the past three years are looked into in some detail, in so far as they exemplify some of the positions in the space of choices defined. The main contribution of the paper is towards a characterization of the language convergence property of deductive database languages which has a key role in addressing critiques of the deductive and object-oriented database research enterprise. A basic familiarity with notions from deductive databases and from object-oriented databases is assumed.