1. A system for optimizing a query, comprising: a memory, and at least one processor operatively coupled to the memory; a construction module executed via the at least one processor and capable of building a data structure for a query, the data structure including a plurality of components, wherein each of the plurality of components corresponds to at least one graph pattern; a flow module executed via the at least one processor and capable of determining a plurality of flows of query variables between the plurality of components; a cost determination and ranking module executed via the at least one processor and capable of determining a combination of the plurality of flows between the plurality of components that results in a minimum cost to execute the query; a constraint module executed via the at least one processor and capable of generating one or more constraints for ruling out invalid flows of the plurality of flows; and an integral linear programming (ILP) solver, wherein the cost determination and ranking module uses the ILP solver to solve a linear optimization problem of determining the combination of the plurality of flows between the plurality of components that results in the minimum cost under the one or more constraints generated by the constraint module; wherein the one or more constraints comprise a component constraint enforcing semantics of an external view of one or more of the components, a graph constraint enforcing semantics of the plurality of flows of query variables, and a predecessor constraint enforcing semantics of one or more potential predecessors.
1. A system for optimizing a query, comprising: a memory, and at least one processor operatively coupled to the memory; a construction module executed via the at least one processor and capable of building a data structure for a query, the data structure including a plurality of components, wherein each of the plurality of components corresponds to at least one graph pattern; a flow module executed via the at least one processor and capable of determining a plurality of flows of query variables between the plurality of components; a cost determination and ranking module executed via the at least one processor and capable of determining a combination of the plurality of flows between the plurality of components that results in a minimum cost to execute the query; a constraint module executed via the at least one processor and capable of generating one or more constraints for ruling out invalid flows of the plurality of flows; and an integral linear programming (ILP) solver, wherein the cost determination and ranking module uses the ILP solver to solve a linear optimization problem of determining the combination of the plurality of flows between the plurality of components that results in the minimum cost under the one or more constraints generated by the constraint module; wherein the one or more constraints comprise a component constraint enforcing semantics of an external view of one or more of the components, a graph constraint enforcing semantics of the plurality of flows of query variables, and a predecessor constraint enforcing semantics of one or more potential predecessors. 3. The system according to claim 1 , wherein the one or more constraints are expressed as a function of decision variables.