- Structure of Search Engines

The services you use when you search for an information source are built up in different ways. The services that let you do the most precise searches are often built on the fact that the descriptions of materials are in different fields on a database record. In one field is a title, in another a date of publication and so on. Because the description is structured in this manner you can also choose to search in only one field or in several fields at the same time.

Advanced searching in unstructured catalogues.

Most search services on the Internet contain resources that is automatically indexed and saved in a database. It is this database that you search in. It is important to understand that when you do a search, you are not searching all the material on the Internet but only copies of a part of this material. How much of the free available material on the Internet is copied and stored in search engines databases differs between the engines. They also reindex their databases with varying degrees of regularity; web pages that change contents will therefore not be shown in their latest version in service until the index has been updated.

A web page is often structured more with consideration to the layout than to the contents. A simple HTML structure usually lets you search for specific file format titles and URL’s, depending on how the web page producer has used the possible functions in HTML. Information such as language and date can be made searchable in separate fields. The information about languages and recent updates can quite simply be put into so called meta-data - information about, for example, a web page or a book. Most web pages though, do not contain much of this information. It is one of the reasons why you sometimes get less relevant hits than what you have searched for. Look under the title Search Engines in the next chapter to bring up different examples of services.

Advanced searching in structured databases.

Meta-data - descriptions of the contents in the database - are also what catalogues with better structures use. Good and trustworthy meta-data can only be created intellectually. Several services in the Internet do this, such as certain different subject portals and most of the databases with articles and other materials that the library has access to. The library’s services and catalogues, both online and card catalogues, work this way. Here you do not have to be sure of whether it is written by or about Strindberg or if the text is about Lotta Strindberg or August Persson instead. This is one of the main benefits of searching a structured catalogue.