Stanford University Libraries

Chemical Literature (Chem 184/284)
University of California at Santa Barbara

Lecture 13: Chemical Abstracts Online, Part II: Subject Searching

Subject Searching in CAS Online

  • Subject searching online can be far more powerful than the equivalent search in print
    • searching is normally far faster
    • you can readily combine concepts
    • you can search by both keywords and subject headings, plus terms from the title, abstract and subject subheadings.
  • Still, the rules for print CA will affect your optimum strategy.
  • For more details and some examples, see How do I search STN? at http://www.cas.org/training/basics/page3.html and Lessons 2, 3, and 4 of Using CAS Databases on STN at http://www.cas.org/ACAD/cover.html

Basic Index in the CA File

  • The CA File Basic Index is composed of words from the title, abstract, assigned keywords (as in the weekly Subject Index), subject headings and subheadings (as in the Volume and Collective Indexes), plus the Registry Numbers for chemical substances.
  • Most subject searches, therefore, just use the Basic Index. If for some reason you wish to be more specific, you can always specify a particular field for searching, e.g. /ti, /ab/, /ct, /it

Search Tips for the Basic Index

  • Use the Index Guide
    As with print CA, checking the Index Guide to see what the standard terminology might be is always a good idea.
  • Use EXPAND
    EXPAND will let you see if a given term is used, how often it appears, and what other forms of the word might be used.
  • Abbreviations
    Remember that terms in the abstracts, keywords and subheadings are heavily abbreviated, but words in the title and main headings are not. Check the abbreviations list and search both the abbreviation and the full form of the term.
    The CA file now affords an easy way to get around this, not available in every file — the command SET ABBREVIATION ON (or SET ABB ON) tells the system to check for abbreviations for any search terms used and incorporate CAS abbreviations as synonyms. See STNote 12 at http://info.cas.org/ONLINE/STN/STNOTES/stnote12.html for an example.
  • Truncation
    Consider using truncation to pick up multiple forms of a term (including abbreviations). Remember, you can use right-hand, internal and left-hand truncation in the CA basic index.

Display Scan: An Easy Way to Check Terminology

  • Most DISPLAYs cost money. However, CA has a free display format which allows you to look at the title and indexing of randomly selected articles from an answer set: DISPLAY SCAN.
  • To take advantage of D SCAN, do a search with your “best guess” terminology. Then enter D SCAN.
  • D SCAN can also display specific fields (ti, hitrn, hitind) if you don't want to see the full indexing.
  • After displaying the first random record, the system will prompt you for how many more records you wish to see. You may repeat this until you have scanned the whole set if you wish. If not, type “0” or “end”.
  • D SCAN will help you
    • evaluate whether your search strategy is on target by examining random titles
    • locate additional synonyms for the key terms you are using
    • discover whether there are terms or concepts which you should exclude (NOT) to eliminate false hits.

Proximity Operator Tips

  • Remember that using AND in the Basic Index will pick up terms from anywhere in the title, abstract or indexing.
  • Generally, search your terms individually, then combine L#’s with a more specific proximity operator. If you find too little, you can always back off to AND.
  • The (S) operator is a good general choice. It will find terms anywhere in the same “sentence”, which is good for terms in the abstract without being too restrictive.
  • The (L) operator also works well but is a bit more likely to pick up bad hits from the abstract.
  • Remember that in the indexing, sometimes your concepts will appear in one order, sometimes in the reverse. Subject headings and subheadings from pre-1997 records frequently use “inverted order” while post-1997 subject headings and subheadings tend to use natural language order.
  • Remember that if you want to search terms as a phrase, you can enter them as you would naturally write them, and Messenger will automatically assume the proper (W) operator to carry out the search.
  • Use the (W) only if you are sure that your terms will only appear in a specific phrase.
  • If you need more specificity than (S), but aren’t sure of word order, use (A) or (nA).

Stopwords

  • Common words like articles (a, an, the) or prepositions (of, by, with, for) are not indexed in the Basic Index. They are termed “stopwords”.
  • Stopwords do count in figuring the distance between words for proximity operators.
  • However, it is sometimes useful to search for certain stopwords as part of a phrase. For example to distinguish between “redn of” and “redn by”. In the CA file, you can search for such stopword-containing phrases in the /IT (for index term) field.
  • An IT search can be combined with other subject searches.

Classification Codes (/cc)

  • Both the 80 subject sections (e.g. “Steroids” or “Physical Organic Chemistry”) and the five broad subject categories (e.g. “BIO” or “MAC”) can be searched in the /CC field.
  • You may use either the section numbers or terms from the name of the section.
  • Classification codes can be useful as a limiting tool:
    • when searching for an author with a common name, limit the search to his/her area of research
    • if you want only a specific kind of study of a class of compound, e.g. physical properties of a compound, but not biological studies.

Substance Searching in the CA File

  • The primary method of indexing chemical substances in Chemical Abstracts Online is the CAS Registry Number.
  • The primary method of obtaining CAS RN's online is through the Registry File, followed by crossover to the CA file.
  • But there are some uses for searching by chemical name in the CA file.

Chemical Names in the CA File

  • Just as in print CA, searches for information on whole classes of compounds suggest use of the name of the class as a search term (esters, aldehydes, steroids, porphyrins).
  • Remember that these terms alone may miss studies of individual members of the desired group.
  • Sometimes, a term may appear in the abstract which the indexer did not feel was important enough to index by RN. This happens frequently with reagents used in synthesis, by-products and the like. They may, however, be in the title or abstract and so be searchable by name.
  • Use left and right truncation if you have a good “root” to use: ?porph?, ?mycin?
  • Searching by a combination of RN and chemical name can be a good idea for maximum comprehensiveness. However, if you’re not using a familiar common name (ethanol), class name (polyanilines) or trade name (aspirin), you may run into nomenclature ambiguities.
  • Remember that Messenger treats punctuation (dashes, periods, commas) as spaces between words

Roles (/rl)

  • The CA file uses a set of codes to indicate the role which an indexed substance or class of substances plays in the indexed document.
  • Some of these roles correspond to the subheadings found in the print Chemical Substance Index (e.g. analysis, uses). Others are more specific.
  • Four letter codes are used for the more generic roles, and three letter codes for the more specific roles.
  • If a specific role has been assigned, a search on the more general role or roles to which it belongs will also find the item.
  • See STNote 5: Target Your Searching with CAS Roles at http://info.cas.org/ONLINE/STN/STNOTES/stnote5.html for more details and a list of role codes.
  • Roles may be searched in the /rl field and linked (L) to chemical class names or Registry Numbers 
    => s fullerenes (L) spn/rl
=> s 88-06-2 (L) biol/rl
  • Or, roles may be used directly as field codes. 
    => s 88-06-2/biol
  • If you aren’t sure about a role code, you can EXPAND in the Roles thesaurus to get a list of the codes and their definitions. 
    => e preparation+all/rl

This page created by Chuck Huber (huber@library.ucsb.edu).

Previous: Lecture 12 | Up: Chem 184 Schedule | Next: Lecture 14