This allows, for instance, linking between the references in the ADS databases and online electronic journals, data tables, and astronomical object lists. Over the years, the ADS databases have been expanded by incorporating references from different sources, while still maintaining information about their origin and grouping. For the articles that fall in this dataset, the ADS provides links to the list of their references and citations. We are working to add more cross-references on a regular basis by cooperating with the publishers of electronic journals in the creation of links to and from them, and by automatically recognizing references from the scanned images of older journal articles. The Abstract Query form allows users to perform sophisticated fielded queries by simply typing the name of the item to be searched for in the proper input field.
Users can submit queries by author, object name, words in the title, and words in the abstract text.
Following an intuitive syntax in use with other search engines, users can require that a particular term be present or missing from the list of results, or can use boolean constructs to formulate each fielded query. Upon issuing a query, the ADS search engine ranks all the publications in the database against the input query by assigning them a relevance score. This score is computed as a weighted sum of the normalized frequencies of the search terms. The search interface provides default weights but also gives users great flexibility by letting them modify the value of such weights. For instance, users can specify to return bibliographies that have appeared only in refereed publications, or only in one or more specific journals.