Online Dictionary of Crystallography talk


From Online Dictionary of Crystallography

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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 first stage of the action of the Working Group was two-fold, on one hand to define the nature and scope of the Dictionary and, on the other hand, to develop an appropriate tool for its implementation.

The purpose of this report is to present the state of the project after nearly one year's experience and to give the Working Group's proposals on these two points and on the financial implications.

Nature and scope


Many definitions of crystallographic terms are scattered in the International Tables but there is, at present, no place where they are systematically compiled, as is the case, for instance, for the chemical terms defined in the various compendia published by IUPAC (the 'gold', 'red', 'blue', 'purple', 'silver' books). The many questions received by the Commission on Crystallographic Nomenclature related to matters of definitions and nomenclature show that there is a real need for such a compendium for crystallography. The idea was received enthusiastically by the Executive Committee in Florence and the Working Group was set up to implement a pilot project for a dictionary of crystallographic terms.


It is proposed that 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. The present form of the project follows the Wikipedia pattern and makes use of the MediaWiki software (see Technical Considerations). It was implemented thanks to the unceasing and highly efficient efforts of the Research and Development Officer, Brian MacMahon.

It will always be possible at a later stage to consider a physical book with a CD containing all the hyperlinks.

Scientific scope

Broadly speaking, the project should be confined to the subject of crystallography, the area of science over which the IUCr has authority. Terms selected for inclusion should have a clear crystallographic implication and terms from connected disciplines (mathematics, physics, chemistry, mineralogy, biology, computational data processing, etc.) 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. 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 and figures are included where necessary (see, for instance, the entry Bragg's law).

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

The granularity of definitions

The Working Group recommends a reference product that is a blend between “dictionary” and “encyclopaedia”: a list of terms with short definitions and cross-links to other entries in the work, with at times longer developments. These longer developments are to be written on a separate page that one accesses via a hyperlink (see for instance the page arithmetic crystal classes). Hyperlinks are also provided to other web resources of the IUCr (Teaching Pamphlets, CIF dictionaries, International Tables, Journals). For instance, in the entry reciprocal lattice, hyperlinks are given to the corresponding pamphlet on the IUCr web site (open access) and to the appropriate chapters of IT Volumes A, B, C and D; for these it is for the Executive Committee to decide (after recommendation from the Finance Committee) whether that link will be free access or not. As other examples, the entry CIF has links to Journal articles (suscribers only or by buying the articles) and the entry Bragg's law to 50 Years of X-ray Diffraction (free access). Hyperlinks to other web sites such as the IUPAC web sites or educational web sites can also be provided, if appropriate (see, for instance the entry absolute structure).

The general pattern of typical page is:

  • translation of the term in other languages,
  • main definition
  • examples or applications or special cases
  • history
  • list of links to other entries or to IUCr or other web pages

Structure of the work

The work will be structured in several ways to assist navigation. The terms are entered alphabetically and can be retrieved alphabetically, but the WiKi software allows an ordering in categories and subcategories. Each entry can be attached to one or more categories (and subcategories). At the time of writing, categories are being assigned to entries on an ad hoc basis in an attempt to determine suitable structuring mechanisms. A click on a category provides links to all the entries related to that category. The present list of categories is given on the Main Page. As an example the subcategory [Twinning] has been introduced in the category [Fundamental crystallography].

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 of 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.

Note that the Wiki software allows searches on headwords, but also full-text searching of the entire corpus, so that the user has available a large number of query-based informational retrieval strategies.

Level of definitions and audience

The primary goal of the dictionary is to be a reference for authors and referees of IUCr Journals and for 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.

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, however, requires that the work should be done under the supervision of a Main Editor or Editor-in-Chief and and a small number of appointed Editors (and subeditors) for the various categories (and subcategories), chosen in priority among the CCN members and consultants.

The initial experience of the Working Group has been, however, that even the greatest enthusiasts for the project are so busy that they find it difficult to spend the time necessary to make substantial contributions. The authoring privilege has been extended recently to the rest of the CCN. Early indications are that, again, the rate of accretion of new definitions is slower than we would like to see. One can but conclude than financial incitation is required if one wants the project to proceed at a reasonable pace.


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 well as to educational resources such as the Teaching Pamphlets and any new educational initiatives arising from the Teaching Commission. As the Online Dictionary of Crystallography would be an important and useful service to researchers, students and authors, it is desirable that it should be open access, bearing in mind that most definitions have links to IT Volumes, which are not open access. This last point may encourage people to subscribe to International Tables Online.

Financial implications

The project as initially envisaged will rely heavily on volunteer labour and existing hardware resources. The current pilot implementation shares the same hardware as the main IUCr web site (although is managed as a separate virtual server, so can easily be moved to its own server machine if required). Some additional software development will be required (e.g. implementation of a reliable backup strategy, modifications to the style to conform with other IUCr web components); but so long as these are not time-critical, they can be absorbed within the existing workload of the R&D department. Significant software developments (such as creation of a hard-copy edition) would need to be assessed and costed separately. Note that hardware costs in the event of a migration to a separate server would be modest (e.g. of the order of GBP 1000 would suffice for a powerful dedicated machine).

Technical editing costs are ruled out at this stage (it is assumed that the invited contributors will have a high degree of literacy, and that there will be a measure of self-regulation as contributors edit each other's entries to correct minor spelling and typographic errors). Since each entry will be presented as a separate web page, minor inconsistencies of style and presentation will not be so important as they would be in a hard-copy publication. Conversely, however, the decision to produce a hard-copy publication would be likely to involve more rigorous technical editing, with subsequent added costs.

The Finance Committee should monitor the possible need for payment of editorial honoraria. It is expected that the project will require an Editor-in-Chief responsible for its overall shape and direction (at present this role is filled by the project initiator, Professor Authier). The roles of such an Editor-in-Chief will also cover the possible appointment of subsidiary editors to supervise the collection of definitions in topic areas where they have particular expertise, and the commissioning of definitions or sets of definitions to address topics not currently covered. The number and roles of secondary editors will depend in part on the readiness of the volunteer pool of contributors to identify deficiencies and provide needed definitions without prompting. The experience of the Wikipedia project suggests that this is possible in principle, but the early experience of the pilot suggests that significant effort will be needed, at least in the early stages, to build an initial critical mass of content that will inspire more active involvement by volunteer contributors. It is intended to return to this point when the project produces its next report. In the mean time, it is not unreasonable to provide conservatively for the appointment of a small number - six to a dozen - of specialist Editors responsible for commissioning content within their fields of expertise, and possibly paid a modest honorarium in recognition of their successes (by analogy in some way with journal editors' handling of manuscripts).

Technical Considerations

APPENDIX: Membership of the Working Group

The initial membership of the Working Group established in Florence consisted of:

  • Andre Authier (Chair)
  • John Helliwell
  • Bill Clegg
  • Paola Spadon
  • I. David Brown
  • Brian McMahon

Giovanni Ferraris, as Chair of the Commission on Inorganic and Mineral Structures, Massimo Nespolo, as Chair of the Commission on Mathematical and Theoretical Crystallography and Peter Strickland, Managing Editor of IUCr publications, as observer subsequently joined the group. Howard Flack also provided sample entries and useful feedback.