1. A method for presenting a data lineage diagram indicating relationships among metadata items stored in a metadata management system accessible to a computing system, the method including: receiving a request that identifies a first metadata item, stored in the metadata management system, from a user interface, the first metadata item including metadata describing first stored data that corresponds to at least a portion of a dataset or an executable program and is stored in a first data source different from the metadata management system; providing a plurality of selection specifications for executing queries from the computing system to select metadata items in the metadata management system that are related to a given metadata item; querying the metadata management system using one or more of the plurality of selection specifications to identify a set of one or more metadata items that are related to the first metadata item, where a first selection specification from the plurality of selection specifications is associated with the first metadata item; for each of multiple returned metadata items in the identified set, querying the metadata management system to identify additional metadata items according to a selection specification from the plurality of selection specifications that is associated with the returned metadata item, including performing multiple iterations of queries, where each iteration includes identifying another set of one or more metadata items each related to at least one metadata item of a previous set of one or more metadata items from a previous iteration, and where iterations of queries are performed until no more metadata items are found that are related to any of the previous sets of one or more metadata items; and generating a data lineage diagram indicating data lineage relationships among programs and data represented by the metadata items identified using the querying, where the data lineage diagram includes nodes that correspond to the programs and data represented by the metadata items and edges that represent the data lineage relationships among the programs and data represented by the metadata items, and the edges include two or more of: an edge representing a data lineage relationship between a node representing the first stored data and a node representing stored data that corresponds to at least a portion of a dataset or an executable program stored in a second data source different from first data source and the metadata management system; an edge representing a downstream data lineage relationship between the node representing the first stored data and a node representing stored data that corresponds to at least a portion of a dataset or an executable program affected by the first stored data, wherein the downstream data lineage relationship enables downstream data lineage tracing to indicate how the first stored data has been used; and an edge representing an upstream data lineage relationship between the node representing the first stored data and a node representing stored data that corresponds to at least a portion of a dataset or an executable program, wherein the upstream data lineage relationship enables upstream data lineage tracing to indicate one or more sources from which the first stored data is derived.