sru

SRU, or Search/Retrieve via URL, is a specification for performing search operations and retrieving metadata records over the World Wide Web. It provides a simple, HTTP-based interface that allows clients to issue a search request and receive a structured result set from a database or repository.

Requests are constructed as URLs using HTTP GET or POST and typically include parameters such as version, operation=searchRetrieve, query (often written in the Contextual Query Language, or CQL), startRecord, maximumRecords, and recordSchema. The server responds with an XML document containing the total number of matching records, the requested records, and diagnostic information if applicable. The record content is returned in a chosen schema, with common options including Dublin Core (dc), MODS, or MARCXML. Some servers also support a queryType parameter to indicate the syntax of the query.

SRU is closely related to the SRW (Search/Retrieve Web Service); SRU provides the URL-based method, while SRW defines a related web service interface. Both are used in libraries, digital libraries, and institutional repositories to expose searchable metadata about catalogs, articles, or other resources. The standard emphasizes interoperability and ease of access, enabling programmatic queries without the complexity of older protocols.

Advantages of SRU include simplicity, stateless requests, and broad compatibility across platforms that support HTTP. Limitations can arise from inconsistent server feature support, varying available record schemas, and incomplete adoption of CQL across implementations. SRU remains a common choice for exposing bibliographic and metadata search functionality in library and digital repository environments.