Web of Knowledge is a collection of databases including
Science Citation Index Expanded, Social Sciences Citation Index, and Arts & Humanities Citation Index are collectively known as the Web of Science (WOS).
What makes Web of Science unique is that it was the first database to include a search feature using the references of a journal article. Because a good paper provides references related to its own topic in its references, those references can be mined for other relevant publications on your topic. And, if you can also search for the papers that cited this paper in their own references, you can assume that those new papers were published on a related topic and they also may be relevant to your topic. Web of Science is designed to take advantage of these relationships to help you find relevant documents, as well as being searchable in traditional ways.
The founder of Web of Science and the originator of the concept of citation searching by database was Eugene Garfield, a chemist. He based his concept on "shepardizing." In law, many decisions about a case are based upon precedent. Shepardizing is the tracking of "publications which have referred to the case, the other court decisions which have affected the case and any other references which may be of value to the lawyer." (Garfield, 1994) Garfield thought this might be useful to the study of science literature.
Eugene Garfield designed Web of Science starting with journal articles in the science disciplines. The sciences publish primarily in journals and have strict criteria regarding the correct application of the scientific method. Therefore, Garfield set very strict criteria for the journal titles that were included. For this reason, Web of Science is most useful to the sciences; less useful to the social sciences; and only moderately useful to the humanities.
One reason for this is that the humanities publish their research as often in books as in journals--WOS only indexes journals. A second reason is that social science and humanities journals have less frequently met the strict criteria that WOS requires for its journal content. The social sciences are less able to apply rigorous scientific methodology to their research for ethical or logistical reasons. For example, you can't not educate a group of children to create a control group for your research. Or you can't manipulate a real business to find out what management methods work best--the company would never allow it. WOS has realized this and is relaxing its standards for social science and humanities journals.
Garfield sold his company to Thomson Reuters and now works as a consultant. He remains active in the sciences and information science disciplines.
Impact factor is a measure developed by Thomson Reuters from data collected from the Web of Science. It is often used as a measure of the importance or impact of a journal's articles on known knowledge.
"The impact factor reflects the number of citations of a journal’s material in the preceding two-year period divided by the number of citable materials (source items) published by that same journal within the same period." (Kurmis, 2003)
The impact factor has received some criticism that the scholarly community has overestimated its importance and is being misused. Other citation metrics have also been developed, including the H-index, the Eigenfactor, and SCImago Journal Rank.
