Can you provide two prominent examples of indexing services and explain their primary function?

1. **Web of Science (Clarivate Analytics):** This is a comprehensive indexing service that covers millions of articles from scholarly journals, conference proceedings, and books across various scientific, social science, and arts and humanities disciplines. Its primary function is to provide extensive citation data, allowing researchers to track the impact of specific articles, authors, or journals, and to discover related research through citation networks. While it includes abstracts, its core strength lies in its meticulous indexing of bibliographic and citation information. 2. **Scopus (Elsevier):** Scopus is another large bibliographic and abstract database for scientific, technical, medical, and social sciences literature. Its primary function is to offer a broad overview of global research output by indexing journal articles, conference papers, and books, along with cited references. It helps researchers find relevant literature, track citations, and analyze research performance through author profiles and institutional affiliations, providing extensive metadata for discovery.