Donald R. Slutz

A history and evaluation of System R

System R, an experimental database system, was constructed to demonstrate that the usability advantages of the relational data model can be realized in a system with the complete function and high performance required for everyday production use. This paper describes the three principal phases of the System R project and discusses some of the lessons learned from System R about the design of relational systems and database systems in general.

Microsoft TerraServer: a spatial data warehouse

Microsoft® TerraServer stores aerial, satellite, and topographic images of the earth in a SQL database available via the Internet. It is the worlds largest online atlas, combining eight terabytes of image data from the United States Geological Survey (USGS) and SPIN-2. Internet browsers provide intuitive spatial and text interfaces to the data. Users need no special hardware, software, or knowledge to locate and browse imagery. This paper describes how terabytes of “Internet unfriendly” geo-spatial images were scrubbed and edited into hundreds of millions of “Internet friendly” image tiles and loaded into a SQL data warehouse. All meta-data and imagery are stored in the SQL database. TerraServer demonstrates that general-purpose relational database technology can manage large scale image repositories, and shows that web browsers can be a good geo-spatial image presentation system.

Support for repetitive transactions and ad hoc queries in System R

System R supports a high-level relational user language called SQL which may be used by ad hoc users at terminals or as an embedded data sublanguage in PL/I or COBOL. Host-language programs with embedded SQL statements are processed by the System R precompiler which replaces the SQL statements by calls to a machine-language access module. The precompilation approach removes much of the work of parsing, name binding, and access path selection from the path of a running program, enabling highly efficient support for repetitive transactions. Ad hoc queries are processed by a similar approach of name binding and access path selection which takes place on-line when the query is specified. By providing a flexible spectrum of binding times, System R permits transaction-oriented programs and ad hoc query users to share a database without loss of efficiency. System R is an experimental database management system designed and built by members of the IBM San Jose Research Laboratory as part of a research program on the relational model of data. This paper describes the architecture of System R, and gives some preliminary measurements of system performance in both the ad hoc query and the “canned program” environments.

System R: an architectural overview

We have described the architecture of System R, including the Relational Data System and the Research Storage System. The RDS supports a flexible spectrum of binding times, ranging from precompilation of “canned transactions” to on-line execution of ad hoc queries. The advantages of this approach may be summarized as follows: 1. For repetitive transactions, all the work of parsing, name binding, and access path selection is done once at precompilation time and need not be repeated. 2. Ad hoc queries are compiled on line into small machine-language routines that execute more efficiently than an interpreter. 3. Users are given a single language, SQL, for use in ad hoc queries as well as in writing PL/I and COBOL transaction programs. 4. The SQL parser, access path selection routines, and machine language code generator are used in common between query processing and precompilation of transaction programs. 5. When an index used by a transaction program is dropped, a new access path is automatically selected for the transaction without user intervention.

Introduction to regenerative simulation

A recently developed method for estimating confidence intervals when simulating stochastic systems having a regenerative structure is reviewed. The paper is basically tutorial, but also considers the pragmatic issue of the simulation duration required to obtain valid estimates. The method is illustrated in terms of simulating the M/G/1 queue. Analytic results for the M/G/1 queue are used to determine the validity of the simulation results.

A note on the calculation of average working set size

Finite-length reference string of arbitrary structure are considered, and an exact expression for average working set size in terms of “corrected” interreference interval statistics is derived. An example is discussed; upper and lower bounds are obtained; and the average working set size function is shown to be efficiently obtained for a set of page sizes, in a single pass of the reference string. This work follows the developments of a paper by Denning and Schwartz, who consider infinite-length reference strings which satisfy certain statistical properties and who derive an expression relating the asymptotic average working set size to the asymptotic missing page rate function under working set replacement.

Generalized working sets for segment reference strings

The working-set concept is extended for programs that reference segments of different sizes. The generalized working-set policy (GWS) keeps as its resident set those segments whose retention costs do not exceed their retrieval costs. The GWS is a model for the entire class of demand-fetching memory policies that satisfy a resident-set inclusion property. A generalized optimal policy (GOPT) is also defined; at its operating points it minimizes aggregated retention and swapping costs. Special cases of the cost structure allow GWS and GOPT to simulate any known stack algorithm, the working set, and VMIN. Efficient procedures for computing demand curves showing swapping load as a function of memory usage are developed for GWS and GOPT policies. Empirical data from an actual system are included.

JANUS: An interactive system for document composition

This paper describes the architecture of a proposed document composition system named JANUS, which is intended to provide support for authors of complex documents containing mixtures of text, line art, and tone art. The JANUS system is highly interactive, providing authors with immediate feedback and direct electronic control over page layouts, using a special two-display workstation. Authors communicate with the system by marking up their documents with high-level descriptive “tags”. A tag definition language is provided whereby new tags may be defined and the format of each tagged object may be controlled.

Regenerative simulation of a queuing model of an automated tape library

Recently, techniques have been developed for estimating confidence intervals when simulating stochastic systems having a regenerative structure. These techniques are applied to the simulation of a queuing model of a computer systems automated tape library. Theoretical and practical issues related to the application of these techniques are addressed. An interesting feature of the automated tape library represented in the queuing model is that certain queues have finite capacity; when these queues are filled to capacity certain services are prevented from occurring. The regenerative techniques are used in conjunction with multiple comparison procedures to make statistically valid statements about the effect of the finite queue capacities on performance.

Flow graph schemata

Flow Graph Schemata are introduced as another uninterpreted model for parallel computation. A modeling example is provided and some results stated concerning decidable problems of determinacy and equivalence.