Cross-reference Information Research Articles

A new aid for teaching the physical basis of remote sensing

Abstract A folded-card slide rule containing cross-referenced information on the electromagnetic spectrum and remote sensing platforms and sensors is described. The slide rule is used in undergraduate level courses in applied remote sensing and has proved to be a useful means of motivating students and encouraging their interest in this area of the subject.

EMBL–Search: a CD–ROM based database query system

This paper describes a system of generally applicable index files provided on the EMBL sequence databases CD-ROM to facilitate the development of front-end software to the sequence databases available on this CD-ROM. The index files are used by a new versatile and user-friendly database retrieval program for the Apple Macintosh, EMBL-Search, which allows the easy construction of complex database queries. EMBL-Search utilizes cross-reference information contained in the databases to support navigation between different information resources. The ability to run EMBL-Search on a local computer network accessing a shared database CD-ROM makes its use particularly cost effective.

The Medina Formation in New York State: a Computer-Assisted Regional Study Using an Integrated Database

Modern personal computers or work stations with access to user-friendly Geological Information Systems software and multilevel geologic databases permit the exploration geologist to extract and display a variety of geologic information in a fraction of the time it would take to compile the same data without the assistance of the computer. Integrated exploration systems include the database, which may be composed of a number of information files, computer programs that have the ability to interrogate any number of the different data files, cross-reference and select specific information, process the data, and present the output as significant visual images, maps, and correlated sections. A study of the Lower Silurian Medina Formation in New York State uses surface information, formation tops, production data, and digital well-log files to present a series of regional views that clearly display the depositional sequence. Maps and cross sections illustrate the development of shorelines, barrier bars, and deltaic deposits. The interactive features of integrated systems allow a geologist to create and capture those pictures that lead to the most likely interpretation.

Tichy's response to R. W. Schwanke and G. E. Kaiser's “Smarter Recompilation”

Schwanke and Kaiser's extension of smart recompilation is an intriguing idea. Their mechanism aims at delaying recompilation work by permitting “harmless” compilation inconsistencies to remain after changes. Full consistency can be reestablished at a later time, after the change has been tested in a subpart of the system. If the change was inadequate, then no needless compilation work was performed. This strategy is used frequently in practice, by exploiting loopholes in system generation tools. Schwanke and Kaiser's mechanism is novel in that it makes this practice safe. The compiler is aware of the inconsistencies, and will not overlook dangerous ones. Furthermore, it can help reestablish full consistency once a change is deemed acceptable. Smarter recompilation defines a harmless inconsistency as follows. If a declaration is changed, this action is treated as introducing a new version of the declaration. The coexistence of both the old and new versions in the same configuration is a harmless inconsistency as long as the uses of the two versions do not conflict. The system must be separable into two partitions, one that uses the old version and the other the new one, such that the interface between the two depends on neither. Since the inconsistent declarations do not cross the interface, the two partitions may even communicate with each other. Of course, inconsistencies not captured by the type system cannot be treated in this way. Schwanke and Kaiser's note leaves a few minor questions unanswered. For instance, a new or changed declaration might cause a redeclaration or overloading error that can only be detected by recompilation. Is this potential problem left undetected until full consistency is desired, or is it checked immediately? If a declaration is deleted that is still in use, is the deletion treated as an error or as a delayed deletion that will take effect after the last use disappears? If the old and new versions of a procedure operate on the same data structure, is it always desirable to let both versions coexist, or can the programmer indicate that the old version should be eliminated before the next program execution? Perhaps a future paper about an implementation will clarify these points. Smarter recompilation also opens the door for more powerful programming tools. For example, since the mechanism maintains cross-reference information, a tool like Masterscope [1] could be built relatively easily. The tool would have the advantage that cross-reference information is immediately available once a module has been compiled. Only little additional data would be needed to classify the uses of symbols. The information could also be exploited by a Maintainer's Assistant. This program helps with reestablishing consistency after changes by suggesting corrections of the affected program parts. For example, it could attempt to make call sites of changed procedures consistent with their headers, update operations on changed record fields, or perform some simple program transformations in response to data structure changes.