An OPAC, Online Public Access Catalog (also called simply Library Catalog) is an online database of materials held by a library or group of libraries. BIBSYS Ask is an Norwegian OPAC.

Reference databases provide literature references. This can be journal articles, reports, books, patents, standards and book chapters. Reference databases offer information about authors, titles and year of publication. Some reference databases also include a short abstract of the literature. NORART - Norwegian journal Articles is an example of a reference database.

Fact databases contain directly applicable information such as definitions and statistics.

Full-text databases contain full-texts such as articles from journals. ATEKST - Full-text Norwegian newspaper articles is an example of a full-text database.

Databases have different limitations:

• Some are limited to one subject, while others cover several subject areas
• Databases have different geographical and linguistic coverage
• They include different types of material
• They cover different time periods

This means that searching in one database isn't always enough. You might have to use several databases to make sure your search covers all necessary aspects.

Several factors determine which databases you ought to use:

• The topic you want information about
• The amount of information you need
• How up-to-date/recent the information is
• Language limitations
• The time required to obtain the material
• Whether you need academic material

You can search for available databases from NTNU University Library's web page