Curriculum:

Such tools have a long history; Hill, Mcllwaine and Williamson (1997) refer to a literature guide for engineers written in 1891. Terminology may be inconsistent; for example, Wexler ( 1988) notes that the second edition of his guide to toxicology resources m ay be described by a librarian as an annotated bibliography and directory, while he prefers to think of it as a sourcebook. A well-known glossary of library terminology, Prytherch (1995) prefers the term ‘subject bibliography' (‘a list of material a b o u t a particular subject or individual'), reserving ‘subject guide' to mean a guide to the shelves of the library. Internet resource listings m ay be term ed ‘virtual libraries' or ‘subject gateways'.

Listings and guides of this sort can take varied forms. Most well known ones are printed products: books and directories; chapters or sections in monographs; journal articles; reports; and conference presentations. Guides in digital form are now increasingly available, predominantly as HTML files, with links to the resources if these are also in HTML form.

Apart from the obvious characteristics of subject topic and physical format, resource listings may be distinguished by three principal characteristics:

• comprehensiveness: to w h at extent does the list aim to cover, and succeed in covering, all significant items within its field of interest; as is noted below, this aspect seems to have chan ged significantly over time

• currency: how often is the guide updated; clearly the Internet subject

gatew ay, typically u pd ate d monthly or more frequently, has the adva n ta g e over the traditional printed tool, updated annually a t best

• annotation: w h at degree of description and evaluation is app lied to the resources listed

With regard to comprehensiveness, although this has often differed greatly betw een guides of roughly the same date, a general trend over time ca n be discerned. Earlier guides, roughly those dating from before 1980, usually m ade some claim to

comprehensiveness; later guides have emphasised selectivity, understood in different ways.

Typical of the claims of earlier guides is that of Yescombe's guide to sources of information on rubber and plastics, com piled in 1966-67:

‘No guide of this kind can hope to be exhaustive, but every effort has been m ade to include all im portant sources and to describe them accurately up to the end of January 1967' (Yescombe 1968, p ix)

A particularly telling, and relevant, example is given by the guide to m edical sources edited by LT Morton and collaborators. The first edition, dating from 1974, makes an unambiguous claim to com plete coverage:

‘This book attempts to provide a comprehensive guide to the general and specialised literature covering the m edical sciences.. Limitations of space have not perm itted a separate chap ter for every branch of m edicine, but readers will find that several of the contributors hove covered their subjects very broadly' (Morton 1974, preface)

By the fourth edition of 1992, the claim was very different:

‘This book is intended to serve as an evaluative guide to the most im portant sources of information that each contributor has recom m ended from

experience of the subject, rather than as a directory of sources' (Morton and G odbolt 1992, preface)

Guides and listings of the 1980s and 90s have emphasised selectivity. Some have focused on illustrating principles, as in Vernon's 1984 guide to m anag em e nt and business literature:

‘This book .. mokes no a tte m p t to cover all aspects of an ever-broadening subject area. It concentrates instead on trying to help peo ple to understand w h at the literature has to offer, the various forms in which it is published and how to find information by using libraries and other sources' (Vernon 1984, p x)

G rog an’s 1970 guide to the literature of science and technology, primarily written for students, shows this a t its logical conclusion, by describing types of resource, giving one or more examples for each:

attention is concentrated on types of literature, and individual titles are normally listed merely as manifestations of those types... where a guide such as this has to be comprehensive is in demonstrating all the types of scientific literature.' (Grogan 1970, p 9 )

Others, recognising the difficulty of com piling guides and lists against a background of rapid ch a n g e in resources, have com bined a focus on basic principles with an a tte m p t to list the most important, or most enduring, tools. Moizell’s 1979 guide to chem ical information is on early exemplar of this trend:

'One of the basic premises on which this book is written is that of ch a n g e .. New and im proved information tools ore constantly being introduced, and, concurrently, older tools becom e less valuable, b e co m e obsolete, or are discontinued. Accordingly, this book presents the most im portant and enduring of the classical tools of chem ical information: the more significant newer tools; and, most importantly, the underlying methods, principles, and keys.. Because this book emphasises the more enduring principles that lead to the most effective use of chem ical information, the coverage of sources, methods and tools is selective.' (Maizell 1979, preface p vii)

Still others, fa ce d with a plethora of potentially relevant resources, hove tried to emphasise less well-known sources, for example Welch and King's 1985 guide to m edical sources:

‘W hat w e have atte m pted is to describe services and publications which we feel should be better known. With some rare exceptions familiar features and works are not covered. In some sections w e have been very selective in order to keep the text to a m anageable size. The wish to draw attention to less familiar material has been the criteria of selection.' (Welch and King 1985, preface p x)

A general trend has been to emphasise selectivity by personal ju dgem ent of the 'best' resources, an idea clearly described by Wexler:

‘This remains a selective list with no a tte m pt m ade to cover exhaustively all available materials. A selective list always assumes a certain

presumptuousness on the author's part in judging some books more deserving than others. I have further risked charges of aud acity by highlighting the books that I deem especially noteworthy with an asterisk. I have no concrete criteria for these judgements other than my personal opinion in examining the texts.’ (Wexler 1988, preface p xv)

'The goal of this revised third edition is to provide an up-to-date selective guide to sources of information in all aspects of toxicology and ancillary fields, such as environmental and occupational health and risk analysis.' (Wexler 2000, preface p xix)

Other listings have atte m pted to list the 'best' or 'quality' resources, using detailed and clearly stated quality criteria. This has beco m e particularly im portant with the adve nt of the world wide web, and the OMNI biom edical resources guide

(http ://w w w .om ni.ac.uk) is a goo d example.

Finally, there is the recent trend to produce subject guides of a highly specific nature. Fitzpatrick (2000) describes resources produced by the US Toxicology and

Environmental Flealth Information Program. Narrowing this ap p ro a ch slightly, Wexler (2001), and Fonger et al. (2000) both describe in detail, resources comprising just the TOXNET service. Kehrer and Mirsalis (2001 ) concentrate on w e b sites for professional toxicology societies, whilst Brinkhuis (2001) describes toxicology information from US government agencies. More specifically, Poore, King and Stefanik (2001 ) refer to toxicology information resources from the US Environmental Protection Agency (EPA).

A further issue is the m ethod of structuring the guide, and of categorising the resources. Virtually all guides, other than the most limited, are categorised in some way; indeed, they must be so, if they are to be usable, but the criteria for structuring are quite varied. Many listings have a d o p te d some form of structuring by primary, secondary, tertiary source, though this is often differently defined. Others use a

structuring by subject speciality, by national origin of resources, or by physical format. Any of these may form a primary division, and some guides have a com plex system of sub-division.

The problem is clearly enunciated by Wexler, who points out that the organisation of such a list is critical in providing efficient access, but that there is no perfect w ay to achieve this.

'It has beco m e considerably more difficult to know how to categorise items.' (Wexler 2000, preface p xix)

He also points out the inherent advantages of a computerised over a printed resource listing, in allowing access according to various criteria, and expresses the hope th a t his book will one d ay be joined by on electronic version.