GB/T 40764-2021 in English

《GB/T 40764-2021地理信息 过滤编码》由TC230（全国地理信息标准化技术委员会）归口，主管部门为自然资源部(测绘地理)。

Scope

This standard describes system-neutral XML and KVP encodings for expressing the syntax of projection, selection and ordering clauses, collectively referred to as query expressions. These components are modular and can be used in combination with other standards or individually. Example 1: GB/T 30169 uses some or all of the above components. This standard defines an abstract component called "Abs trac tQue ression (abstract query expression)", and other specifications can subclass specific query elements based on yExpr to implement query operations. This standard also defines another abstract query yExp component called "Abs trac tAdhocQue rresison (abstract immediate query expression)". It is derived from Abs trac tQue reression, and other specifications can subclass specific query elements according to the following query modes: the abstract query element in the yExp service specification can subclass a specific query element, allowing customers to specify a list of resource types, An optional projection clause, an optional selection clause, and an optional ordering clause to query for a subset of resources that satisfy the selection clause. This mode is called an ad hoc query mode, and it differs from stored query expressions that can be invoked by name or identifier because the server does not know about the query until it is submitted for processing. This standard also describes system-neutral XML and KVP encodings for expressing selection clauses. XML representations are easily validated, parsed, and converted to a server-specific language that needs to return or modify object instances for persistent object storage. Example 2: An XML-encoded filter expression can be converted into a WHERE clause in a SQL SELECT statement to obtain data stored in a SQL relational database. Similarly, XML-encoded filtering can be converted into an XPath (XML path) or XPo inter (XML pointer) expression for retrieving data from an XML document. This standard defines XML encoding for the following predicates: a) Standard set of logical predicates: and (and), or (or) and not (not). b) Standard comparison predicate set: equal lt o (equal to), no tequa lt o (not equal to), les st han (less than), les st hano r equal lt o (less than or equal to), great rt han (greater than) , great rt hano requa lt o (greater than or equal to), like (similar), i snu ll (empty) and be twe en (between). c) Standard set of spatial predicates: equal l (equal), disoint (distance), t ouche s (connection), within (included), over rl aps j (overlap), crosses (cross), intersects (intersect), c on tai ns (contain), wi thi naspe cifi edd ist anc e (distance contained within), beyondspe cifi edd ist anc e (distance beyond), and BBOX (bounding box). )(,d standard set of time predicates: after later than) be fore (before),beg i ns (begin later than),begunby (start earlier than),con tai ns(before later than),du ri ng (later than earlier than), ends (later than end), equal ls (equal), me ets (followed), me t by (reverse followed by), over rl aps (earlier than overlap) and over rl appliedby (overlap later than). e) A predicate that tests whether an object identifier matches a specified value. This standard defines the XML encoding of metadata that allows services to declare supported conformance classes, predicates, operators, operators and functions. These metadata are called filtering capabilities (Fi lterCapab ilities). 2 consistency