Syntax and Semantics of the Stack Based Query Language.2x

The Stack-Based Architecture (SBA) is a formal methodology addressing object-oriented database query and programming languages. In SBA we reconstruct query languages’ concepts from the point of view of programming languages (PLs). The approach is motivated by our belief that there is no definite border line between querying and programming; thus there should be a universal theory that uniformly covers both aspects. SBA offers a unified and universal conceptual and semantic basis for queries and programs involving queries, including programming abstractions such as procedures, functions, classes, types, methods, views, etc. SBA assumes a semantic specification method that is referred to as abstract implementation. It is a kind of operational semantics where one has to determine precisely on an abstract level all the data structures that participate in query/program processing and then to specify the semantics of all the languages’ operators in terms of actions on these structures. SBA introduces three such structures that are well-known in the specification of PLs: (1) an object store, (2) an environment stack, (3) a query result stack (thus the stack-based architecture). These structures are fundamental for precise semantic description of everything that may happen in database query/programming languages. In particular, classical query operators, such as selection, projection, joins and quantifiers, can be generally and precisely specified using the above three abstract structures, with no references to classical database theories such relational/object algebras or calculi. SBA introduces a model query/programming language SBQL (Stack-Based Query Language). In our intention SBQL plays the same role as relational algebra for the relational model, but SBQL is incomparably more powerful. The power of SBQL concerns a wide spectrum of data structures that it is able to serve and complete algorithmic power of querying and manipulation capabilities. At the same time, SBQL is fully precise with respect to the specification of semantics. SBQL has been carefully designed from the pragmatic (practical) point of view. We were struggling severely with parasite syntactic sugar, redundant operators and semantic reefs (when human intuitive semantics does not match machine semantics). The pragmatic quality of SBQL is achieved by orthogonality of introduced data/object constructors, orthogonality of all the language constructs, object relativism, orthogonal persistence, typing safety, introducing all the classical and some new programming 1 This research is supported by the Polish Ministry of Science and Higher Education through the grant N N516 3755 34.