Unfolding of Conjunctive Queries Using Context Free Grammar for Parsing

Abstract

There are two different notations for queries over relational databases throughout the thesis. The first is SQL, which is the language used to query relational data in commercial relational systems. SQL is a very complex language. For our discussion, we typically used only its most basic features such as selecting specific rows from a table, selecting specific columns from a table, combining data from multiple tables usingthejoinoperator,takingtheunionoftwotablesandcomputingbasicaggregation functions. Secondly, we used the notation of Conjunctive Queries, which is based on mathematical logic. Lexical analysis is the extraction of individual words or lexemes from an input stream of symbols and passing corresponding tokens back to the parser. If we consider a statement in a programming language, we need to be able to recognize the small syntactic units (tokens) and pass this information to the Yacc generator. We need to also store the various attributes in the symbol or literal tables for later use, e.g., if we have an variable, the tokenizer would generate the token var and then associate the name of the variable with it in the symbol table. In this case, the variable name is the lexeme. The tokenization process takes input and then passes this input through a keywordrecognizer,anidentifierrecognizer,anumericconstantrecognizerandastring constant recognizer, each being put in to their own output based on disambiguating rules. Our goal was to unfold Conjunctive Queries. We successfully implemented our production rules and tokenization process. The rest of our task is to implement unfolding Conjunctive Queries with C language and merge with Yacc generator. So, we are hopeful that we will be able to unfold Conjunctive Queries in future.