No abstract available.

No abstract available.

article Free Access Share on Is multiple inheritance essential to OOP? (panel) Authors: Yen-Ping Shan View Profile , Tom Cargill View Profile , Brad Cox View Profile , William Cook View Profile , Mary Loomis View Profile , Alan Snyder View Profile Authors Info & Claims ACM SIGPLAN NoticesVolume 28Issue 10Oct. 1, 1993 pp 360–363https://doi.org/10.1145/167962.165923Published:01 October 1993Publication History 3citation781DownloadsMetricsTotal Citations3Total Downloads781Last 12 Months30Last 6 weeks2 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF

This work investigates one aspect of the performance of CODASYL database systems: the data reference behavior. We introduce a model of database traversals at three levels: the logical, internal, and physical levels. The mapping between the logical and internal levels is defined by the internal schema, whereas the mapping between the internal and the physical levels depends on cluster properties of the database. Our model explains the physical reference behavior for a given sequence of DML statements at the logical level. Software has been implemented to monitor references in two selected CODASYL DBMS applications. In a series of experiments the physical reference behavior was observed for varying internal schemas and cluster properties of the database. The measurements were limited to retrieval transactions, so that a variety of queries could be analyzed for the same well-known state of the database. Also, all databases were relatively small in order to allow fast reloading with varying internal schema parameters. In all cases, the database transactions showed less locality of reference than do programs under virtual memory operating systems; some databases showed no locality at all. No evidence of physical sequentiality was found. This suggests that standard page replacement strategies are not optimal for CODASYL database buffer management; instead, replacement decisions in a database buffer should be based on specific knowledge available from higher system layers.

This paper compares the database model specified by the CODAYSL Data Definition Language Committee in its 1978 Journal of Development and the prior model, known familiarly as the CODASYL DBTG model, as specified in 1973 and 1971. The primary achievement of the 78 model appears to be increased potential for data independence by separation of external model and internal model considerations. The external model is described by a DDL; the internal model is described by a DSDL. Additionally, there is enhanced potential for data integrity via more explicit expression of data integrity constraints in the DDL. Conversion of a database from 73 model CODASYL DBMS support to 78 model support is discussed with emphasis on DSDL capabilities. The range of options in the DSDL open to the database designer for specifications of internal storage structures is surveyed. Several conclusions are drawn regarding implementation of support for the 78 model.