This chapter describes the steps necessary to

• upgrade an existing OPC HDA application with OPC UA capability
  
• create a new OPC HDA / UA client application

OPCHDA.NET-UA based applications can access OPC HDA and OPC UA servers, even concurrently.
What server is accessed is determined by the server identifier;

• for OPC UA servers the server identifier has the format:       UA:url
  e.g.   ua:opc.tcp://localhost:62849/Advosol/uaPLUSsim
  See below for a detailed description of the url format.
  
• For OPC HDA server the identifier is a DCOM ProgId
  e.g. Advosol.SimDAServer.1
  The ProgId identifier is exactly as it used to be. The restriction is that is must not start with "UA:"

UA Server URL format

OPCHDA.NET-UA based applications work with OPC HDA and UA servers. The server accessed depends on the server identifier string.
For UA server access the identifier has to have the format:     UA:url
otherwise it's used as an OPC HDA ProgId for the access to an OPC HDA DCOM server.

The UA server URL  has the format:   scheme://host:port/name
e.g.   http://localhost:80/Advosol/uaSim
         opc.tcp://localhost:62849/Advosol/uaSim