The DELTA format (DEscription Language for TAxonomy) is a flexible and powerful method of recording taxonomic descriptions for computer processing. It has been adopted as a standard for data exchange by the International Taxonomic Databases Working Group.
The DELTA System is an integrated set of programs based on the DELTA format. The facilities available include the generation and typesetting of descriptions and conventional keys, conversion of DELTA data for use by classification programs, and the construction of Intkey packages for interactive identification and information retrieval. The System has been developed in the Natural Resources and Biodiversity Program of the CSIRO Division of Entomology over a period of 20 years, and is in use worldwide for diverse kinds of organisms, including viruses, corals, crustaceans, insects, fish, fungi, plants, and wood. The programs are continually refined and enhanced in response to feedback from users.
The DELTA System is capable of producing high-quality printed descriptions. DELTA data can include any amount of text to qualify or amplify the coded information, and this text can be carried through into the descriptions. Common features can be omitted from the data and the descriptions, while remaining available for identification and analysis. There is extensive control over the combination of attributes into sentences and paragraphs, the omission of repeated words, and the insertion of headings. The most important or diagnostic attributes (derived automatically or manually) for each taxon can be emphasized in full descriptions, or short descriptions containing only these attributes can be produced. The descriptions can be fully typeset without the requirement for any manual editing. These features are exemplified in books such as ‘The Grass Genera of the World’ (CABI International: Wallingford), which was generated automatically from a DELTA database, and contains descriptions of about 800 genera in terms of more than 500 characters.
The DELTA program Key generates conventional identification keys. In selecting characters for inclusion in the key, the program determines how well the characters divide the remaining taxa, and balances this information against subjectively determined weights which specify the ease of use and reliability of the characters. Keys can be tailored for specific purposes by adjusting the weights, restricting the keys to subsets of the characters and taxa, and changing the values of parameters that control various aspects of the key generation. For example, keys could be produced for particular countries or climates; using only vegetative, floral, or fruit characters; starting with important characters; or biased towards common species.
DELTA data can easily be converted to the forms required by programs for phylogenetic analysis, e.g. Paup, Hennig86, and MacClade. The characters and taxa required for these analyses can be selected from the full data set. Numeric characters, which cannot be handled by these programs, are converted to multistate characters. Printed descriptions can be generated to facilitate checking of the data, and Intkey can be used for further data checking, and for finding differences, similarities, and correlations among the taxa.
The interactive identification and information retrieval program, Intkey, offers better and more comprehensive features than any similar program. These features include: entry and deletion of attributes in any order during an identification; calculation of the ‘best’ characters for use in identification; the ability to allow for errors (whether made by the user or in the data); the ability to express variability or uncertainty in attributes; optional display of notes on characters; direct handling of numeric values, including ranges of values and non-contiguous sets of values; the ability to alter the treatments of unknowns, inapplicables and overlapping values, as required for different applications (flexibility in this respect being particularly significant in relation to identification versus information retrieval); retrieving free-text information (that is, information not encoded in terms of the character list); freedom to carry out operations in any order (for example, displaying taxon descriptions or differences during the course of an identification); automatic handling of characters that become inapplicable when other characters take certain values; restricting operations to subsets of characters or taxa; defining keywords to represent subsets of characters and taxa; locating characters by included words, and taxa directly by name; no limits on numbers of taxa, characters, and character states; no limits on lengths of taxon names and character definitions; specifying ‘character reliabilities’ appropriate for particular purposes; obtaining lists of taxa possessing or lacking particular attributes or combinations of attributes; preparing lists of taxa uncoded for particular characters or sets of characters; listing similarities or differences between taxa, with the ability to vary the interpretations of ‘similarity’ and ‘difference’; describing taxa in terms of nominated sets of characters; generating diagnostic descriptions for specimens or taxa, to specified degrees of redundancy; coalescing descriptions (e.g. to generate accurate generic descriptions from species descriptions); user-definable toolbar buttons to represent any command or sequence of commands; input of complex or lengthy sequences of commands from files; selective output of results to files; generating files suitable for input to other DELTA programs (for example, to highlight diagnostic features in printed descriptions); screen display of illustrations of characters and taxa; no limit on size or number of colours in illustrations; scaling and scrolling of illustrations; simultaneous viewing of several illustrations; overlaying text on illustrations; selection of character states from illustrations; complete on-line help; normal and advanced modes of operation; and acceptable response times with large sets of data.
To produce descriptions, keys, and Intkey packages in different languages, it is only necessary to translate the character list. Data sets have been produced in Chinese, Dutch, French, German, Greek, Indonesian, Italian, Portuguese, and Spanish. The Intkey program itself can readily be translated into other languages, as all of the program text (menus, commands, prompts, diagnostic messages, and help) are in simple text files separate from the program files. English, French, German, Italian, and Spanish versions are currently available.
The DELTA Mailing List and the DELTA Newsletter are media for discussion of descriptive databases. Topics include: computer programs for taxonomy, data formats, data interchange standards, data capture, data analysis, database design, description printing, expert systems, information retrieval, interactive identification, keymaking, mapping, and taxonomic characters.
Dallwitz, M. J. (1980). A general system for coding taxonomic descriptions. Taxon 29, 41–6.
Dallwitz, M. J., Paine, T. A., and Zurcher, E. J. (1993 onwards). ‘User’s Guide to the DELTA System: a General System for Processing Taxonomic Descriptions.’ 4th edition. http://biodiversity.uno.edu/delta/
Dallwitz, M. J., Paine, T. A., and Zurcher, E. J. (1995 onwards). ‘User’s Guide to Intkey: a Program for Interactive Identification and Information Retrieval.’ 1st edition. http://biodiversity.uno.edu/delta/
Dallwitz, M. J., Paine, T. A. and Zurcher, E. J. (1998). Interactive keys. In ‘Information Technology, Plant Pathology and Biodiversity’, pp. 201–212. (Eds P. Bridge, P. Jeffries, D. R. Morse, and P. R. Scott.) (CAB International: Wallingford.)
Development of the programs has been supported by grants from the Australian National Parks and Wildlife Service, and the National Science Foundation of the United States of America (Award Number 9631047).
We are grateful to many colleagues for supplying diverse data and ideas, which have guided the development of the coding system and the associated programs.
We thank J. Humphries for providing space on the Biodiversity and Biological Collections Web Server.