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Sometimes a transaction control language (TCL) [1] is argued to be part of the sub-language set as well. DQL statements are used for performing queries on the data within schema objects. The purpose of DQL commands is to get the schema relation based on the query passed to it.
Although a schema is defined in text database language, the term is often used to refer to a graphical depiction of the database structure. In other words, schema is the structure of the database that defines the objects in the database. In an Oracle Database system, the term "schema" has a slightly different connotation.
SELECT is the most complex statement in SQL, with optional keywords and clauses that include: The FROM clause, which indicates the table(s) to retrieve data from. The FROM clause can include optional JOIN subclauses to specify the rules for joining tables. The WHERE clause includes a comparison predicate, which restricts the rows returned by ...
A number of representational phrase structure theories of grammar never acknowledged phrase structure rules, but have pursued instead an understanding of sentence structure in terms the notion of schema. Here phrase structures are not derived from rules that combine words, but from the specification or instantiation of syntactic schemata or ...
The terms schema matching and mapping are often used interchangeably for a database process. For this article, we differentiate the two as follows: schema matching is the process of identifying that two objects are semantically related (scope of this article) while mapping refers to the transformations between the objects.
A primary division for the discussion of clauses is the distinction between independent clauses and dependent clauses. [3] An independent clause can stand alone, i.e. it can constitute a complete sentence by itself. A dependent clause, by contrast, relies on an independent clause's presence to be efficiently utilizable.
A dependent clause, also known as a subordinate clause, subclause or embedded clause, is a certain type of clause that juxtaposes an independent clause within a complex sentence. For instance, in the sentence "I know Bette is a dolphin", the clause "Bette is a dolphin" occurs as the complement of the verb "know" rather than as a freestanding ...
The process of checking to see if a XML document conforms to a schema is called validation, which is separate from XML's core concept of syntactic well-formedness.All XML documents must be well-formed, but it is not required that a document be valid unless the XML parser is "validating", in which case the document is also checked for conformance with its associated schema.