Abstracting and Indexing (A&I) services are essential part of publication process. The journal indexes content at the article level by assigning subject headings (descriptors or keywords) to each one and then making them searchable in the product’s database. These services also index other bibliographic elements of journal articles, including authors, titles, date of publication, etc.
(Recently, some A&I services have even begun to index at more granular levels, including, for example, indexing individual images.) Today, most journals require that their authors compose an abstract (a summary) of their article, so A&I services generally don’t compose abstracts anymore — they simply create a searchable database with subject, author, and title access to individual articles from a selection of journals they choose to include in their database.