Report of Working Group

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The Dictionary Working Group of the Commission on Crystallographic Nomenclature (CCN) was formed during the 20th IUCr Congress in Florence to provide guidance on the establishment and conduct of a project undertaken under the aegis of the Commission, with the approval of the IUCr Executive Committee and the involvement of other Commissions and appropriate bodies of the IUCr, to provide online definitions of terms used in the practice of crystallography. The remit of the Working Group covered the following topics:

1. Is the project to be and to remain an online project (web URLs)?

Or should a book form be also envisaged in the future (question by Henk Schenk, Chairman of the IUCr/OUP book Committee)?

2. The scientific scope of the project

Broadly speaking, the project should be confined to the subject of crystallography, the area of science over which the IUCr has authority. However, crystallography is used by, and merges with, very many other areas of chemistry, physics, mathematics, materials science, biology, computational data processing, etc.. What criteria should be applied for deciding which terms to include within the project, and which to exclude? (Consider, for example, the detailed descriptors for protein secondary structure included in the mmCIF dictionary. Should the online "crystallography dictionary" include definitions of protein folds, beta sheets etc.?)

  • Should the names of compounds (minerals, materials, chemical or biological compounds) be included?
  • Should physical concepts be included (entropy, energy, etc.)?
  • Should mathematical terms be included? (group properties, tensor properties, etc.)
  • Should there be translations of each entry in other languages (French, German, Spanish, Russian, Chinese, Japanese)? See old “red” International Tables as an example.
  • Should names of people be included (Bravais, Bragg, Ewald, Laue, etc.) be included?
  • Should reference to computer programs be included?
  • How should double-word items be included: “neutron interferometry”, “X-ray interferometry”, or “interferometry (neutron)”, “interferometry (X-ray)”?
  • Should specialized expressions such as “normalized structure factors” be itemized as such or appear within the definition of “structure factor”? (there are many such examples).
  • Should equations be included?

3. The granularity of definitions

What is the appropriate amount of text for each entry in the compilation? (This may determine, among other things, the name of the project - glossary, dictionary, index, thesaurus, encyclopaedia?) From Longman's Dictionary of the English Language:

  • glossary: a list of terms (e.g. those used in a particular text or in a specialized field), usually with their meanings
  • dictionary: a reference book containing words, usually alphabetically arranged, together with information about them, especially their forms, pronunciations, parts of speech, meanings, origins, grammatical requirements, and idiomatic uses
  • index: a guide or list to aid reference: e.g. an alphabetical list of items (e.g. topics or names) treated in a printed work that gives for each item the page number where it appears, or a list of items of a specified type
  • thesaurus: 1. a book of words or of information about a particular field or set of concepts; especially a book of words grouped according to their meaning. 2. a list of subject headings or index terms, usually with a cross-reference system for use in the organization of a collection of documents for reference and retrieval
  • encyclopaedia: a reference work that contains information on all branches of knowledge or treats comprehensively a specified branch of knowledge, usually in articles arranged in alphabetical order of subjects either in a single list or within each of several large subsections
  • compendium: a full list or inventory (Webster), a book containing a list of useful hints (Collins); as an example see the IUPAC gold book ( a list of names, each one with hyperlinks.

What is the quantity of illustrations to be given (drawings, diagrams, spectra, photographs, etc.)

Should the work be organized in Categories and Subcategories?

4. The level of definitions

Should this be a reference work for authors and referees of IUCr Journals, research professionals, undergraduate students, high-school students, the general public? Can it be designed as a multi-level resource?

5. Delegation of authority and labour

What is an appropriate editorial structure to commission, review and implement definitions? This needs to take into account the involvement of Commissions, the possibility of different educational levels for the completed work, and perhaps some technical aspects of presentation and online editing.

6. Presentation

Some consideration should be given to broad aspects of how the project will be presented: as a single web site, as multiple sites (perhaps appropriate if different educational levels are supported), as a free resource or a potential source of revenue, as a companion to International Tables?

7. Financial implications

The project as currently envisaged in its project definition phase will rely heavily on volunteer scientist labour and existing hardware resources, but there may be a need for editorial honoraria, or other costs that the Working Group can specify, such as hardware, technical editing, secretarial help, etc. The Working Group will report its findings to the Finance Committee.


The project should be executed initially as solely an online project because of the flexibility of the online medium, the fact that there is no limit on the number of entries, the possibility of hyperlinks to IUCr and other web resources. It is possible to consider at a later stage a physical book with a CD containing all the hyperlinks.

Scientific scope

Terms selected for inclusion should have a clear crystallographic application. Terms from connected disciplines (mathematics, physics, chemistry, mineralogy, biology) should be included insofar as they relate to crystallography, e.g. “crystallographic group”. Names of chemical or biological substances or minerals should not be included at the present stage, but terms such as “albite twin law” should.

The Working Group agrees that translations of terms in other languages than English should be given, but not of their definitions.

Reference to computer programs per se should not be included, but there might be instances when it becomes essential, e.g. SHELX.

Names of people should only be included if they relate to crystallographic concepts, e.g. “Bragg’s law”, “Ewald sphere”.

Double-word items such as “X-ray interferometry” should be entered as such. A search on “interferometry “ will automatically retrieve them.

Equations should be included.

The number of entries is not predetermined. There is no technical limitations requiring this and the project can grow with time. The Working Group will start with a small number of terms in order to get the pilot project operational. The project will then be open the whole Commission on Crystallographic Nomenclature and a number of 500 terms should easily be reached when the web pages are first opened to the public. If the idea is successful, it will probably grow to some thousands of distinct terms over the years.

Granularity of definitions

The Working Group recommends a reference product that is a blend between “dictionary” and “encyclopaedia”, what the French call a “dictionnaire encyclopédique”: a list of terms with short definitions and cross-links to other entries in the work, with at times longer developments. For instance, “reciprocal lattice” will have a short definition and a hyperlink to the corresponding pamphlet on the IUCr web site (open access) and to the appropriate chapter of IT Volume B; the entry “Bragg’s law” should give the law with a drawing and its derivation could be obtained via an appropriate hyperlink.

Links to ComCIF dictionaries should be provided where appropriate.

The work may be structured in several ways to assist navigation. The terms will be entered alphabetically and can be retrieved alphabetically, but the WiKi software allows an ordering in categories (and eventually in subcategories). Each entry can be attached to a category (and a subcategory). These categories could correspond for instance to titles of IT Volumes, but with additional subjects (“mathematical crystallography” etc.); subcategories would correspond to Chapters. A click on a category entry will provide links to all the entries related to that category.

As an example, to get the entry “Grüneisen relations”, one may either click on that term, or click on the Category “Physical Properties”; thzt will provide links to subcategories, one of them being “Thermal expansion”; a click on that subcategory will provide a list of links to all the entries related to that topic, one of them being “Grüneisen relations”. The entry “Grüneisen relations” will give a definition and hyperlinks to Chapters 1.4 and 2.1 of International Tables Volume D.

There are several advantages to having categories and subcategories. One is to allow searches on areas of interest, for instance if you are looking for a particular type of twinning, but don’t remember its exact name. Another one is to make the work preparing the dictionary easier by assigning editors and subeditors to categories and subcategories. Their duty would be to oversee the definitions and to check that there are no obvious omissions.


The primary goal is to be a reference for authors and referees of IUCr Journals and to research professionals in general: it will give the “official” IUCr acceptance of terms. As such it will also be useful to students and to the general public.

The work forms part of a multi-level resource in the sense that besides the short definition hyperlinks will be provided either to a longer definition or to appropriate existing IUCr resources. It will complement International Tables.

Organization of contributors

The Editorial Board should consist of the members of the CCN, with representatives from the other Commissions as consultants for the various fields of crystallography. It is clear that, as Editors of the various IUCr publications, the members of the CCN are the people whose duty is to say how crystallographic terms should be used. Efficiency requires that the work should be done under the supervision of a Main Editor and Editors (and subeditors) for the various categories (and subcategories), chosen among the CCN members and consultants.


It is expected that the resource would appear as a single web site. However, it should also act as a companion to International Tables and to the Journals. As the Online Dictionary of Crystallography would be an important and useful service to the researchers and authors it is desirable that it should be open access, bearing in mind that most definitions will have links to IT Volumes, which are not open access. This last point may incite people to suscribe to International Tables Online.

Financial implications

The project as currently envisaged will rely heavily on volunteer labour and existing hardware resources, but there may be a need for editorial honoraria, or other costs such as hardware, technical editing, secretarial help, etc. to be identified by the Working Group and reported to the Finance Committee.


A Pilot Project with about 500 entries should be implemented and guidelines for further development as well as an estimation of its financial implications provided in time for the Finance Committee meeting in 2006 (usually around March).