Simple and efficient implementation of pattern matching in MOLA tool

One of crucial problems for model transformation implementations is an efficient implementation of pattern matching. The paper addresses this problem for MOLA tool implementing the model transformation language MOLA. Another goal has been to keep the implementation as simple as possible. The paper presents one possible solution to the combined problem where an SQL database with fixed schema is used as the MOLA runtime repository. A natural coding is selected where a MOLA pattern match can be mapped to a single non-standard self-join SQL query. The paper shows that a sufficient matching efficiency can be obtained this way. The generated queries are analyzed from the table join order point of view and it is shown that the default query optimization for the MySQL database can find an order close to optimal. This analysis and performed experiments are used to conclude that at this moment MySQL is the most fit for MOLA implementation among "free" relational databases. In addition, benchmark tests based on a simple natural model transformation problem are used to estimate efficiency of the selected implementation architecture and to compare MOLA tool to the popular graph transformation tool AGC. Benchmark tests confirm the efficiency of the current MOLA tool implementation and applicability of MOLA language to MDD-specific tasks