Citations include information such as author, title, source, and abstract, but do not contain the full-text of or images in the article. Developers must maintain certain quality standards, especially the integrity of the data in each citation. The goal of this review is to give users an appreciation for the differences between implementations so they can make a more informed decision about which service to use.
Boolean systems can take a while to master.
NLP systems work in a variety of ways. Relevance is determined by the frequency that the search terms appear in the document, where they appear, and other factors such as the publication date. NLP systems are often easier to learn than Boolean systems, because they require no knowledge of Boolean search techniques. MeSH terms number about 45,000 and are organized in a hierarchy. The assignment of a particular MeSH term to an article denotes the presence of that medical concept in the article.