All queries against a graph database require a node (or a collection of nodes) as a starting point. Rather than referencing nodes through their identity numbers, you typically select nodes by specifying a value for one or more properties. For example, in the organization database, if you want to find all the employees that report directly to a particular manager, you would provide a property value (such as the payroll number) that identifies that manager as the starting point.
In most graph databases, you can define indexes over properties to enable the database server to quickly locate a node based on the values of these properties. In particular, you should create indexes over each of the properties that you use to specify the starting criteria for the searches that your application performs. In the organization example, if you wish to retrieve the employees that work for the manager with the Payroll_Number property of 1004, you should create an index over this property. If you are using Neo4j and the Cypher query language, you can then use the following code to retrieve the employees (this example assumes that the index is called Payroll_Number_Index)