There are different types of search tools... not always easy to fit into a specific category.
Encyclopedia Britannica gives the following general definition of database: "any collection of data, or information, that is organized for rapid search and retrieval by a computer. Databases are structured to facilitate the storage, retrieval, modification, and deletion of data in conjunction with various data-processing operations. A database management system (DBMS) extracts information from the database in response to queries. Database records and files must be organized to allow retrieval of the information. Queries are the main way users retrieve database information. The power of a DBMS comes from its ability to define new relationships from the basic ones given by the tables and to use them to get responses to queries. Typically, the user provides a string of characters, and the computer searches the database for a corresponding sequence and provides the source materials in which those characters appear; a user can request, for example, all records in which the contents of the field for a person’s last name is the word Smith." Since the databases used for searching academic publications most often contain bibliographic (i.e. title, authors, abstract, keywords...) information they are often called bibliographic databases.
In databases that contain academic publications you will find quality assured publications, mainly research articles, but also conference publications, academic books and chapters from academic books and sometimes quality checked web sites.
A Web search engine produces a list of “pages”—computer files listed on the Web—that contain the terms in a query. Most search engines allow the user to join terms with and, or, and not to refine queries. The Web is largely unorganized, and the information on its pages is of greatly varying quality, including commercial information, national databases, research reference collections, and collections of personal material. Search engines try to identify reliable pages by weighting, or ranking, them according to the number of other pages that refer to them, by identifying “authorities” to which many pages refer, and by identifying “hubs” that refer to many pages. These techniques can work well, but the user must still exercise skill in choosing appropriate combinations of search terms.
Search engines use crawlers, programs that explore the Web by following hypertext links from page to page, recording everything on a page (known as caching), or parts of a page, together with some proprietary method of labeling content in order to build weighted indexes. Web sites often include their own labels on pages, which typically are seen only by crawlers, in order to improve the match between searches and their sites. Abuses of this voluntary labeling can distort search results if not taken into account when designing a search engine. Similarly, a user should be cognizant of whether a particular search engine auctions keywords, especially if sites that have paid for preferential placement are not indicated separately. Even the most extensive general search engines, such as Google, Yahoo!, Baidu, and Bing, cannot keep up with the proliferation of Web pages, and each leaves large portions uncovered (from Encyclopedia Britannica).
The most common search engine for academic publications is Google Scholar (GS), which has access to millions of academic publications, BUT GS has not any quality assurance system of its own. Thus, there is a bigger risk of finding low-quality publications using GS, but you also may find the same publications in GS as you do in the quality controlled databases.
Since the number of electronically available library resources have increased, libraries nowadays use so called discovery tools to make it easier for users to discover and access these resources. The discovery tools can search many e-resources simultaneously via a query from a single search box. In most cases, discovery services only allow access to resources that a library is authorized to use through paid subscriptions, open access licenses, or the public domain (Breeding, 2014).
Breeding, M. 2014. Web-Scale Discovery Services: Finding the right balance. [ https://americanlibrariesmagazine.org/2014/01/14/web-scale-discovery-services/ ] Accessed August 15 2017.
A library catalogue contains information about the different books and journals available at the library. In a "modern" library catalogue there are often possibilities to make reservation for books and ask for books to be transported between different libraries within a library network. In a library catalogue you can search for titles, authors/editors, and sometimes keywords and index of books but, usually, you CAN'T search for articles in a library catalogue.
- Use Google scholar as complement or to find specific articles.
- Use search engines for other information like governmental reports and websites.