This library helps you to build an [openCypher](http://www.opencypher.org/) query layer on top of a relational database or structured data in data lakes. By leveraging this library, you can transpile openCypher query into a target query language used by the relational database. We have provided a sample target language renderer for [T-SQL](https://docs.microsoft.com/en-us/sql/t-sql/language-reference?view=sql-server-2017).
Originally we built this library to support querying the petabyte-scale Windows 10 telemetry data assets in the [Azure Data Lake](https://azure.microsoft.com/en-us/solutions/data-lake/) as a [Property Graph](https://neo4j.com/developer/graph-database/#property-graph). We chose openCypher because it is a declarative query language resembling SQL, which most our data consumers are already familiar with.
* A openCypher parser built on top of ANTLR4 and the official openCypher grammar to parse and create an [AST](https://en.wikipedia.org/wiki/Abstract_syntax_tree) to abstract the syntactical structure of the graph query;
* A logic planner transforms the AST into relational query logical plan similar to the [Relational Algebra](https://en.wikipedia.org/wiki/Relational_algebra);
* A query code renderer produces the actual query code from the logical plan. In this repository, we provides a T-SQL renderer.
The above components form a pipeline where the openCypher query and the graph schema is fed to the parser and the transpiled query is the output from the code renderer:
Transpiler is tested using the T-SQL target renderer and its results are compared against what is produced by Cypher from the [Neo4j Graph Database](https://neo4j.com/graph-database). Each test compares the query results from the transpiled query on [Microsoft SQL for Linux](https://www.microsoft.com/en-us/sql-server/sql-server-2017) against Cypher on Neo4j 3.x to ensure they are consistent in term of data type and contents.
To run the tests, simply run under the project root folder:
