For example, an application that has a web server and database (i.e., a two-tier application) may be described using two  nodes (one to host the web server and another to host the database).  The author may want both Compute nodes to be instantiated with similar properties such as url, security, etc.

To accomplish this, the author would describe the reusable properties using a named anchor in the “dsl_definitions” section of the TOSCA Service Template and reference the anchor name as an alias in any node templates where these properties may need to be reused.