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Overview of the DELTA System

27 December 2010

M. J. Dallwitz


The DELTA System

The DELTA format (DEscription Language for TAxonomy) is a flexible and powerful method of recording taxonomic descriptions for computer processing. It was adopted as a standard for data exchange by Biodiversity Information Standards (TDWG).

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 was developed in the CSIRO Division of Entomology during the period 1971 to 2000. It is in use worldwide for diverse kinds of organisms, including viruses, corals, crustaceans, insects, fish, fungi, plants, and wood. The programs are free for non-commercial use.

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 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 key program, Intkey, is easy to use and has powerful features, including:

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 latest versions of the DELTA programs, and several data sets, are at the following URL’s.

Support and discussion

DELTA-L is a mailing list for support of programs that use DELTA data, and for general 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, key making, mapping, and taxonomic characters.

DELTA authors

Mike Dallwitz (general correspondence)

Toni Paine

Eric Zurcher

Leslie Watson


The publications that should be cited depend on the components being used, as follows.

Intkey: Dallwitz 1980; Dallwitz, Paine, and Zurcher 1993; Dallwitz, Paine, and Zurcher 1995; Dallwitz, Paine, and Zurcher 2000.

DELTA format, Confor, Dist, Intimate: Dallwitz 1980; Dallwitz, Paine, and Zurcher 1993.

Key: Dallwitz 1974; Dallwitz 1980; Dallwitz, Paine, and Zurcher 1993.

DELTA Editor: Dallwitz 1980; Dallwitz, Paine, and Zurcher 1999.


For a complete list, see Applications and Documentation of the DELTA System.

Dallwitz, M. J. 1974. A flexible computer program for generating identification keys. Syst. Zool. 23: 50–7.

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.

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.

Dallwitz, M. J., Paine, T. A. and Zurcher, E. J. 1999 onwards. User’s guide to the DELTA Editor.

Dallwitz, M. J., Paine, T. A. and Zurcher, E. J. 2000 onwards. Principles of interactive keys.


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 the Institute of Botany, Chinese Academy of Sciences, for hosting the DELTA Web site, and Lisong Wang for providing support. Previous versions were hosted by the University of Michigan, the University of New Orleans, the University of Kansas, and Cornell University, and were supported by Julian Humphries and Jim Beach.

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