Two major flaws in the CODASYL DDL 1973 and proposed corrections

In a schema written in CODASYL DDL 1973, it is syntactically correct to describe an attribute of an entity either by declaring a data item in the record of the entity or by declaring a CODASYL set type in which the record, describing the entity, is a member record. This is considered a major flaw, because extension of a database or integration of two existing databases will then lead to either reprogramming or inconsistency, or both. Examples are described to illustrate situations which occur with a dynamic database. This flaw in the CODASYL DDL 1973 can easily be corrected by requiring that all attributes are represented as a data item in the (logical) schema.

In the CODASYL DDL 1973, there are five places to optionally declare a record identifier, and four of these five places are not in the record but in the CODASYL set type. Declaring record identifiers therefore results in fairly complex and non-orthogonal declarations. This could be simplified by abandoning these five places and by introducing a record identifier clause in the record type entry. For integrity reasons, it is necessary to require that at least one record identifier is declared in every record type entry.

The previous two corrections will make it possible to design a CODASYL set selection clause which is considerably simpler than the existing CODASYL set selection clause, still providing the same functional capabilities.

The examples which were used to illustrate the first flaw are also described in schemas and programs using a DDL in which the two flaws are corrected.

The conclusion is: the corrected DDL is functionally equivalent, yet offers more data independence, is simpler and more orthogonal. Or, said in other words this article concentrates on the major issue of the “great debate” between the network (CODASYL) and relational data base approach. At the end of studying this article the reader is supposed to comprehend the major portion of the contents of the “great debate”.     

A clustering method to distribute a database on a grid

Clusters and grids of workstations provide available resources for data mining processes. To exploit these resources, new distributed algorithms are necessary, particularly concerning the way to distribute data and to use this partition. We present a clustering algorithm dubbed Progressive Clustering that provides an “intelligent” distribution of data on grids. The usefulness of this algorithm is shown for several distributed datamining tasks.     

O^2D^2B系统中的水平划分及分布查询处理

现有的较成熟的分布式数据库系统大都是不含水平划分的,而水平划分能够提高许多数据库操作的时空效率。本文介绍O~2D~2B中包含水平划分的分布式查询处理,主要包括与查询语句相关各表的分布地址集的获得、数据传输费用的计算与执行地点的选择,其中着重介绍通过对查询语句where子句条件表达式的分析,如何得到表的分布信息。与一般水平划分不同的是,O~2D~2B支持多属性划分,并且在划分中可以有重叠包含关系。因此,O~2D~2B具有更强的适用性。     

Distribution Design of Logical Database Schemas

The optimal distribution of a database schema over a number of sites in a distributed network is considered. The database is modeled in terms of objects (relations or record sets) and links (predefined joins or CODASYL sets). The design is driven by user-supplied information about data distribution. The inputs required by the optimization model are: 1) cardinality and size information about objects and links, 2) a set of candidate horizontal partitions of relations into fragments and the allocations of the fragments, and 3) the specification of all important transactions, their frequencies, and their sites of origin.     

A functional approach to database updates

PFL is a functional database language in which functions are defined equationally and bulk data is stored using a special class of functions called selectors. It is a lazy language, supports higher-order functions, has a strong polymorphic type inference system, and allows new user-defined data types and values to be declared. All functions, types and values persist in a database. Functions can be written which update all aspects of the database: by adding data to selectors, by defining new equations, and by introducing new data types and values. PFL is “semi-referentially transparent”, in the sense that whilst updates are referentially opaque and are executed destructively, all evaluation is referentially transparent. Similarly, type checking is “semi-static” in the sense that whilst updates are dynamically type checked at run time, expressions are type checked before they are evaluated and no type errors can occur during their evaluation.

In this paper we examine the expressiveness of PFL with respect to updates, and illustrate the language by developing a number of general purpose update functions, including functions for restructuring selectors, for memoisation, and for generating unique system identifiers. We also provide a translation mechanism between Datalog programs and equations, and show how different Datalog evaluation strategies can be supported.     

A persistent complex object database language

To support a number of emerging applications we propose a persistent complex object database language which is “value” based. The object space is built through the set and tuple object constructors, with practically no normalization constraints on the nesting levels. The proposed persistent database language can serve both as an interface language to the database management system in itself or as the target language of a conceptual data language. Some of the features of the language include: (i) Notion of “path's” capturing logical references to retrieve and update the persistent database, (ii) a rich set of allowable schema types, including disjuncts, and (iii) a collection of powerful operator constructors for sets.     

Parsing an extension to CODASYL FORTRAN DML

The FORTRAN data manipulation language specified by CODASYL requires that parameters be identified by keywords and appear in a prescribed order. These restrictions can largely be removed. A method of parsing the resultant data manipulation language using database structures is described.     

Distributed database design—Optimization vs feasibility

This paper is concerned with the problem of optimal assignment of data to sites in a distributed relational database. It is shown that in general the optimal allocation will require exponential time in terms of the input. Several heuristic algorithms that can be applied to various constraints and which provide feasible, near optimal results, as well as a model that determines the “best” assignment for a given input out of several optimal and near optimal assignments have been developed. The model is shown to be efficient, to require polynomial time, to be practical in terms of feasible inputs and to achieve assignments with near minimal global and local costs.     

A system for multibody analysis based on object-relational database technology

An efficient support for computational technology and information management will be critical in future Engineering Information Systems (EIS). This paper shows how it is possible to provide efficient data management capabilities to the discipline of Multibody System (MBS) analysis. The MECHAMOS prototype of a MBS analysis tool has been developed that is based on an object-relational database management system, AMOS, which has been extended with additional mathematical functionality by the use of Matlab and MapleV as computational engines. The MBS model is represented as a database model in AMOS and the analysis is based on symbolic formulation of Kane's equations of motion. With this configuration, data is made fully accessible via the AMOSQL query language of AMOS. Furthermore, by providing the MBS application with general database technology, the data management will be more efficient in terms of handling large amounts of data and the development and maintenance of MBS analysis systems. Since MBS models are represented in a “neutral format”, the reusability of these models increases and they will be more persistent to changes in the EIS environment.     

An automatic physical designer for network model databases

Systems EROS is a physical design tool for CODASYL database systems which covers a large spectrum of decision variables, notably location mode, set implementation, set order, and search keys. System EROS is based on a model where the CODASYL physical database design problem is formulated as an extension of the index selection problem in the relational database environment. Optimization algorithms for index selection are extended to solve the more complex problem of selecting a good physical access path configuration for CODASYL databases. The proposed approach represents a unified solution to the physical database design problem for both CODASYL and relational systems     

A structure for expert systems maintenance

An approach to the design of maintainable expert systems is presented. Central to this approach is a conceptual model in which the data and knowledge are both modelled as formal “items” in a uniform way. “Objects” are introduced as “item building” operators. The notion of the “decomposition” of items and objects provides the foundation for a single rule of normalization. This single rule applies to all items and objects, including knowledge items, and is a non-trivial generalization of the traditional normal forms for database. Coupling relationships represent the necessary maintenance paths in the conceptual model. A complete characterization of coupling relationships is given, and the value of normalization to the reduction of maintenance costs is discussed.     

A storage structure definition language for Codasyl Data Bases

This paper proposes a language for the definition of the physical storage structures in a Codasyl Data Base.The language is based on the idea of using a generalized model of the storage structures, called Virtual Paged Memory, which is capable of expressing many of the features which characterize the storage structures of many existing systems. This model is used as an intermediate level between the DDL-schema and the physical database.A critical comparison between the proposed approach and the BCS/CODASYL DDLC DBWAG proposal for a tentative standard of a storage schema definition language is also presented.     

Abstractions for distributed programming

The StarMod language is designed to provide its users with abstractions for distributed computations. The language is based on Wirth's definition of a “module” as impiemented in Modula. The paper discusses abstraction mechanisms for distributed access control and scheduling: in addition, several examples are used to illustrate these concepts.     

Performance issues in dataflow machines

Issues affecting the performance of dataflow computers at the machine and language levels are explored. It is suggested that performance is dictated by the nature and the means of identification, distribution and control of workload in the hardware system. Dataflow is an asynchronous concurrent notation based on fine-grain message-passing in graphical programs. Dataflow machines comprise multiple processing elements and structure store modules connected together via a packet-based switching network. Workload is in the form of finegrain data packets which trigger instruction-level activity in the various components of the hardware architecture. Workload is identified by a compiler for a high-level, single-assignment language, and is distributed across the hardware components dynamically at run-time. The amount of work at any instant can be controlled by a parallelism “throttle”. The paper studies the performance of one example of a dataflow computer, the Manchester Dataflow Machine (MDFM).     

Natural language access to information systems. An evaluation study of its acceptance by end users

The question is asked whether it is feasible to use subsets of natural languages as query languages for data bases in actual applications using the question answering system “USER SPECIALTY LANGUAGES” (USL). Methods of evaluating a natural language based information system will be discussed. The results (error and language structure evaluation) suggest how to form the general architecture of application systems which use a subset of German as query language.     

基于分布结构自适应筛选的数据库存储优化设计

通过对数据库的存储结构优化设计,提高数据库的吞吐量。传统方法采用存储节点校验数据适应度分区的数据库存储模型,数据库中存在重复冗余数据,不能自适应滤除,导致数据存储开销较大。提出了一种基于分布结构自适应筛选的数据库存储优化模型,首先进行数据库的存储机制和分布式数据结构分析,采用相空间重构方法进行存储空间的结构分布重组,采用分布结构自适应筛选方法对提取的数据信息流进行重复冗余数据滤波处理,改善数据在数据库存储空间中的结构分布,实现数据库存储优化。仿真结果表明,采用改进的方法进行数据库构建,能提高数据库存储吞吐量,降低数据存储开销,提高数据库的访问和调度性能,展示较好的应用价值。