Online Public Access Catalogue (OPAC)

Over the past decade, ever-increasing number of libraries is in the process of abandoning the traditional card catalogue as a means of access to their collections and switching over to computer-based catalogue. This phenomenon is characterized as transition from manual methods to mechanical method in the design and development of Online Catalogues, it knows as OPAC.

Through the online public access catalogue (OPAC) now functions against a background of alternative information-gathering technologies it is likely to remain at the center of library operations for the foreseeable future as the primary automated point of connection between library users and those information resources which the library owns. OPACs have a necessary role in preserving access to library collections, maintaining, consistent and authoritative form of bibliographic control and providing a targeted information environment for specific client groups.

It is computer based and supported library catalogue designed to be accessed via terminals so that library users may directly and effectively search for and retrieve bibliographic records without the assistance of a human intermediary. OPAC usually allows searching by author name, title, and subject. OPAC proved access to the library’s holdings via a computer monitor, replacing the traditional card catalogue.

OPACs were introduced in the US in the late seventies and in the UK in early eighties. These have also been introduced in a few libraries. In India libraries have adopted mostly in-house developed software in the design and development of OPACs.

Definitions of OPAC:

The Hildreth (1985) defines Online Public Access Catalogue (OPAC) as follows: “It is time to start thinking of the online public access catalogue as an intelligent gateway to diverse, integrated information specialist and the library patron or and user; a gateway accessible not only in libraries but at places of work. Study; leisure, and the home. Perhaps someday the online catalogue will just be called ‘my online library”.

The ALA GLOSSARY defines Online Public Access Catalogue (OPAC) as follows: “A computer-based and supported library catalogue (bibliographic database) designed to be accessed via terminal so that library users may directly effectively search for retrieve bibliographic records without the assistance of a human intermediary such as a specially trained member of the library staff’.

Simon Smith defines as: “An OPAC (Online Public Access Catalogue) is an online bibliography of a library collection that is available to the public. OPAC developed as stand alone catalogues often form VT100 terminals to main-frame. Library catalogue with arrival of the interest most libraries have made their OPAC accessible from a server to users all over the world”.

According to Harold Glossary defines as: “The catalogue of a library or information centre made available to users online and generally providing a varied of additional facilities such a loan information, online reservations and library news with the demise of the card catalogue the need for stressing the ‘online public access’ part has disappeared and they are new frequently just catalogues”.

Online Dictionary for Library and Information Science (ODLIS) defines as: “An acronym for online public access catalogue a database composed of bibliographic records describing the books and other material owned by a library or library system, accessible via public terminals or workstations usually concentrated near the reference desk to make it easy for user to request the assistance of a trained reference librarian. Most online catalogs are searchable by author, title subject and keywords and allow users to print, download or export records to an e-mail account”.

SIRSI GLOSSARY of terms defines OPAC as: “A computer workstation used to search a library’s catalogue can refer to either the actual workstation in the library, or to the interface provided by the library that is accessible from anywhere”.


Development of OPAC:

Since their emergence, OPACs have undergone large scale improvements but the basic contention remains their accessibility by library clientele without any formal training. In the light of their functions, capabilities, OPACs according to Hildreth have developed through the following three generations:

a) First-generation OPACs.

b) Seconds-generations OPACs

c) Thirds-generations OPACs.

a) First generations OPACs: Phrase searching OPACs’, as they are generally called, were in a way the machine readable forms of conventional catalogues providing such access points as class mark, author, title , subject as phrase and simple left to right phrase matching. Such systems had certain obvious drawbacks, for the probability of exact matching between search phrases with indexing terms was rather small: Much of the computer capabilities were wasted as the system worked like a card catalogue. It was not user-friendly as user/system interaction was quite limited.

b) Second-generation OPACs: Most of the existing OPACs are still at this stage. Influenced by the commercial bibliographic database, second generation OPACs have adopted many of their features likes ‘online help messages’, `alphabetical index displays’ for searching search terms and using `Boolean logic’ for their combination and effective retrieval.

Despite the improvements, the second generation OPACs have made the first generation, Hildreth regards them as ‘deficient tools’ for effective subject searching, for the following reasons:

❖ They offer little or no help in translation of entry query terms into the vocabulary used in the catalogue;

❖ They provide no help to the user in making alternate search statements and techniques, when the initial approach fail;

❖ They do not in all cases lead to a successful free text search(e.g. of the title words); to the corresponding subject headings or class numbers assigned to a broader range of related material;

❖ The retrieval records are generally devoid of such information as table of contents , abstracts and book reviews, that might help user to judge the usefulness of the documents;

c) Third-generation OPACs: The above listed deficiencies were investigated and some of the remedies that emerged were incorporated into third generation OPACs to enhance their subject searching capability. These systems are enriched by the inclusion of additional controlled and uncontrolled access points. Queries are accepted as a ‘natural language’ statement eliminating the need for the user to know quarry formulation and search techniques. Some of the systems use partial match techniques instead of Boolean operators. The retrieved sets are sometimes ranked according to the query relevance. These catalogues ensure vastly improved search system interaction at every level of the search process.

Subject Access in OPAC:

Subject searching in online catalogues requires the translation of user’s Information need into the terms that have been used in the system’s vocabulary. They are then put in some specific statements in the command language of the online catalogue, matched system’s vocabulary retrieve the records to be delivered to the users. During this process, not all the subject searches are one hundred percent successful. They result sometimes in ‘no retrieval’ or ‘too many’ records. So that the users will be discouraged to proceed furthers. In case user suffers these two problems ‘search failure’ and ‘Information overloaded’.

B. Search Failure: A search failure, generally deemed to be a search that retrieves nothings, is not always that obvious. If the retrieved items do not best serve the users needs, the search will be no better than a failure. However, a successful search depends upon the perfect coordination between the users and the system. Any major deficiency on the part of either of the two, results in search failure.

Users are always not to able formulating their search according to the terminology of the system. Difficulties in formulating a search strategy involve problems of syntax, semantics, choice of access points and how to narrow or broaden a search, etc. Therefore, follows that users’ lack of knowledge, doing misspelling and mistyping account for a few causes of search failure. Markey suggests either educating online catalogue users about search strategy and providing in built instructions in the system.

B. Information Overloaded: Information overloaded refers to phenomenon of the retrieval of too many references in response to a subject search so that a users actually gets be wildered and frustrated and may choose not to go further few reason given below:

a) The search term may be too broad.

b) The number of items indexed under a given term might be increasing, as an online catalogue database grows. This increase may be more rapid in a keyword approach then in a subject heading approach.

c) Truncation of items as compared to exact search terms results in higher recall.

d) Boolean OR operator often created the problem of information overload. For example, a request ‘A or B or C’ will retrieve document indexed by any one of these terms as well as documents indexed by all of them.


Searching through OPAC:

The OPAC system has changed the traditional concept of access drastically. It allows multi-dimensional searches providing as a many access points as the data elements depending on the software used. It is an advantage over the linear search provisions in the earlier forms of catalogue. OPACs, allow searches through the access points as author, title, subject, class, keyword, combination etc. OPACs in some modern software provide additional provision of truncation of terms is also available in the OPAC system. This option makes the system most flexible. Two types of searches are possible

i) Simple search;
ii) Complex search

i) Simple search:

  • Author: The search for a document through OPAC is very easy is the name of the author is known to the user. Generally, the last name of the author will be the entry element.
  • Title: Searching for documents by title is similar to searching by author. For title search, users have to select the title option in the menu and type the words in the title of the document. The initial articles are often omitted. In the OPAC system in modern software, users need not type the complete words in the title as the computer will list a certain number of titles in the alphabetical order.
  • Class Number: The Search using the class number requires the user’s knowledge of the class number of a particular subject. For an exhaustive search for document in a subject, class number search is useful.
  • Keyword: Many OPAC systems in modern library software provide keywords search option. This greater flexibility of access to the bibliographic records. In key work search, documents can be searched after using a single word appearing in the name of the author, title Subject or abstract /content depending on the details given in the database. Keyword searching has the flexibility to allow the user to create simple searches and yet a allows the experienced user to build sophisticated searches through precision searching and filtering. Precision Searching provides enhanced control through expanded keyword search capabilities using the following tools:

• Keywords

• Phrase searching

• Full text searching

The disadvantage of the keyword search is that system will relieve some last relevant document as well.

ii) Complex search:

Boolean operators (AND, OR, NOT) a backbone of almost all information retrieval systems including OPACs, through usually considered good for retrieval for exploiting only a potion of information potentially available in the systems. Some main objectives given below:

  • AND Logic: If two terms in a search strategy are linked using the logical operator AND then the output will be the items in which both the terms are used in title or the abstract. This increases the specificity and ensures greater precision, which means only relevant documents will be listed on the computer screen as a result of the search.
  • OR Logic: The Or logic helps the user to search for documents using alternate terms. If two terms are linked using OR logic in a search strategy the output will be a list of documents which contain any one of these terms in title or abstract/content.
  • NOT Logic: The use of NOT logic is to exclude particular terms. The output of such search will exclude documents which contain the term right to the operator NOT in the search strategy.

The Boolean AND operator often results in search failure. For example, a search for ‘A and B and C’ will retrieve records that have all these three terms and will reject those with one or two of these terms. Boolean logic is rigid in nature, for a user making a search ‘A and B’ cannot indicate that the term A is more important for his search than B or vice verse. Documents are either retrieved are either retrieved or rejected, with no middle ground. Ranking of retrieval documents according to the degree of relevance to the inquiry is not possible.

As an alternative to a Boolean search operator, some partial matching techniques. Techniques in this category are used to compare queries with documents represented as index terms. The document representatives are derived from the text of the documents. Features can have weights associated with term. The query terms expressed in natural language or with help of the indexing vocabulary. The retrieval techniques are based on formal models of document retrieval and indexing, viz. vector space, probabilistic and fuzzy sets. These techniques when tested experimentally provided better results than Boolean Systems.


The truncation option gives the searcher the opportunity to search on parts of words by putting an arbitrary symbol. This arbitrary symbol indicates the missing letters in a term. The computer will select all possible alternatives to that missing place. When the technique of truncation is used, the computer will select all the terms with a common roof or common fragments. There are four types of truncation-right truncation, left truncation, simultaneous left and right truncation and infix truncation (middle truncation).

Words truncated with an asterisk (*):

Designate one or more characters

Example Searches                Retrieves

Farm*                                     farm, farms, farming, or other words starting With farm

wa*n                                      Walton, warden, Washington, etc.

This option opens wide possibilities to the users when the exact spelling of a term is not known.


Access Points and Level of Usage of OPAC:

OPAC has been the most common tool for library users and librarians, and it will be also commonly used in digital libraries. It is obvious that well designed GUI improves user-friendliness especially for novice users. Various access points provided in OPAC enables the user to locate document as well as to filter the query for obtaining result of an advanced search. Advanced search provides details of the documents that satisfy particular features or characteristics. Question was asked to disclose the access points generally used by the respondents. Choices were given and users were allowed to specify the access points used by them. The most used search key is the author and is followed by the title and the subject. Words in the title was also found to be made use by many users while the usages of other points were too limited.

Advantages of Online Public Access Catalogue (OPAC):

The ‘Karen Markey’ lists the following advantages of the OPAC

  • To enable a person to find a book of which another, the title or the subject is known.
  • The library patrons need not wander from one place to other to follow see and see also reference.
  • The patrons need not wear out pencils copying the bibliographic information, printers or down loading software provide convenience and ensure accuracy in the transfer of information.
  • It is no longer necessary for a person to come to the library to use the catalog. The catalog can be wherever they are, and they can use it whether or not library itself is open.
  • It addition to that, the catalog can be as up-to-date, as the holdings it represents.
  • The contents for the catalog are no longer restricted to the holdings of the particular library. Theoretically, there is no limit to the number of libraries the online catalog can represent.


Awareness of the user of the Online Public Access Catalogue (OPAC):

Library OPACs are the primary key to the resources of a computerized library. It has many advantages over the traditional card and other forms of catalogue and is extensively being made use in modern computerized libraries. Apart from providing several access points for search, OPAC has provisions to entertain several complex search queries. Online catalogue is one of the first areas of services provided by computerized libraries. All the libraries under study have their OPAC and it was observed that they are maintaining the traditional catalogue also as these traditional catalogues are also still found to be used by many. A question was asked to the users in order to check their awareness about the existence of OPAC in their respective university library as the traditional card catalogues are also in use.

Features of Online Public Access Catalogue (OPAC):

Online Public Catalog must provide searching and locating features for your online public access catalog. Specifically, OPAC offers the following key features.

  • Patrons can perform various levels of searching such as Browse, Heading, keyword, Control number, and Expert.
  • Patrons can select which index they wish to search such as title, author, and subject.
  • Patron empowerment such as searching/viewing of own patron record.
  • Filtering of searches.
  • Browse searches are accumulated on tabs.
  • Access to record views such as Full, MARC, Holdings,


Limitations of Online Public Access Catalogue (OPAC):

1. Do not provide online thesaurus aids useful for subject focusing/identifying terms that are broader or narrower than topic of search.

2. Do not automatically assist the user by providing alternative formulation of the search statement when the initial approach fails.

3. Do not provide sufficient assistance in the translation of the query terms into the vocabulary used in the catalogue.

4. Do not lead the searcher from successful free-text search terms (e.g. titles words) to the corresponding subject headings or class numbers assigned to a broader range of related materials.

5. Do not provide open-ended, exploratory browsing through pre-established linkages between records in the database, in order to retrieve materials related to those already found.

6. Do not rank the retrieval sets in decreasing order of probable relevance to the user’s search criteria.

Reference Article:

  • Sadaf, F. (2015). Application and utility of OPAC in Maulana Azad library.

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