Take Your First Steps with the SAP HANA Graph Engine

Our graph dataset describes the London street network. Formally, a graph consists of nodes/vertices and edges/links/connections. In this case, you have street segments stored in the LONDON_EDGES table, and junctions in the LONDON_VERTICES table. The edges in the graph are “directed”, they have a SOURCE and a TARGET.

Most streets in the real world are bi-directional and so most of the segments are represented as two edges in the graph - one for each direction.

The SAP HANA Graph engine requires a key on both tables, and the source and target of the edges must not contain NULLs.

To ensure the graph’s consistency, it is also good practice to have a foreign key relationship defined on source and target column. Doing so will prevent “dangling edges”, i.e. edges without vertices.

Once your data is prepared, you expose it to the SAP HANA Graph engine via a GRAPH WORKSPACE.

Add primary keys on the tables LONDON_EDGES and LONDON_VERTICES using these statements:

ALTER TABLE "LONDON_EDGES" ADD PRIMARY KEY("ID");
ALTER TABLE "LONDON_VERTICES" ADD PRIMARY KEY("osmid");

Then, add foreign keys on the SOURCE and TARGET column of the table LONDON_EDGES by executing these statements:

ALTER TABLE "LONDON_EDGES" ALTER("SOURCE" BIGINT NOT NULL REFERENCES "LONDON_VERTICES" ("osmid") ON UPDATE CASCADE ON DELETE CASCADE);
ALTER TABLE "LONDON_EDGES" ALTER("TARGET" BIGINT NOT NULL REFERENCES "LONDON_VERTICES" ("osmid") ON UPDATE CASCADE ON DELETE CASCADE);

The Graph Workspace exposes your data to the SAP HANA graph engine. It is a kind of a “view” into your data. In this case, the Graph Workspace is defined directly on the tables. Note that you can also use SQL views, table functions, and remote tables as data sources. You can define multiple Graph Workspaces in one system.

Create the Graph Workspace on the tables LONDON_EDGES and LONDON_VERTICES by executing this statement:

CREATE GRAPH WORKSPACE "LONDON_GRAPH"
	EDGE TABLE "LONDON_EDGES"
		SOURCE COLUMN "SOURCE"
		TARGET COLUMN "TARGET"
		KEY COLUMN "ID"
	VERTEX TABLE "LONDON_VERTICES"
		KEY COLUMN "osmid";

To get a glimpse of your network, you can right-click the LONDON_GRAPH workspace to launch the Graph Viewer.

You now have successfully defined constraints on your tables LONDON_VERTICES and LONDON_EDGES and created a GRAPH WORKSPACE. You are all set up to start working with the Graph Engine now!

In the next tutorial, learn how to use a GRAPH Procedure to calculate Shortest Paths on the street network.