tailieunhanh - RELATIONAL COMPLETENESS OF DATA BASE SUBLANGUAGES

For this tutorial, you must install ArcGIS Desktop (ArcEditor or ArcInfo license level), SQL Server Express, and the ArcTutor data for this tutorial on your computer. Use the ArcSDE for SQL Server Express Installation wizard provided on the ArcGIS Desktop installation media to install an instance of SQL Server Express and enable it to create ArcSDE geodatabases. To complete the installation, follow the instructions in the ArcSDE for SQL Server Express installation guide, which is also included with the ArcGIS Desktop media. You most likely already have ArcGIS Desktop installed, but if not, follow the instructions in the ArcGIS Desktop installation guide to complete this. If the. | RELATIONAL COMPLETENESS OF DATA BASE SUBLANGUAGES by E. F. Codd IBM Research Laboratory San Jose California ABSTRACT In the near future we can expect a great variety of languages to be proposed for interrogating and updating data bases. This paper attempts to provide a theoretical basis which may be used to determine how complete a selection capability is provided in a proposed data sublanguage independently of any host language in which the sublanguage may be embedded. A relational algebra and a relational calculus are defined. Then an algorithm is presented for reducing an arbitrary relation-defining expression based on the calculus into a semantically equivalent expression of the relational algebra. Finally some opinions are stated regarding the relative merits of calculus-oriented versus algebra-oriented data sublanguages from the standpoint of optimal search and highly discriminating authorization schemes. RJ 987 17041 March 6 1972 Computer Sciences 1 1. INTRODUCTION In the near future we can expect a great variety of languages to be proposed for interrogating and updating data bases. When the computation-oriented components of such a language are removed we refer to the remaining storage and retrieval oriented sublanguage as a data sublanguage. A data sublanguage may be embedded in a general purpose programming language or it may be stand-alone -- in which case it is commonly called a query language even though it may contain provision for simple updating as well as querying . This paper attempts to establish a theoretical basis which may be used to determine how complete a selection capability is provided in a proposed data sublanguage independently of any host language in which the sublanguage may be embedded. The selection capability under discussion is a basic non-statistical one. In a practical environment it would need to be augmented by a counting and summing capability together with the capability of invoking any one of a finite set of library .