Information required by the client from the Server includes
- Recipes existing on the vision system (identified by their ExternalIds)
- The assignment between recipes on the vision system and ProductIds
- Recipes currently prepared on the vision system (identified by their ExternalIds)
- Preparedness of a particular recipe (identified by its ExternalId)
- ExternalId of the recipe to a particular ProductId
Note that the OPC UA server is merely a view on the underlying vision system. How a vendor distributes recipe and identification management between the vision system and the server is implementation-defined and outside the scope of this specification.
As long as all data required by the client is available through method calls, it is not actually necessary - although possibly desirable - to expose this information in the OPC UA server Address Space. The OPC UA server will then have to execute a vision system function to retrieve the requested information and return it in an output parameter of the method. For example, the list of recipes existing on the vision system may be requested by a client using a method like GetRecipeListFiltered instead of being read directly from the Address Space.
Exposing meta information on recipes in the Address Space has the consequence that the data is kept in two places, i.e. in the OPC UA server Address Space and in the vision system itself. In this case the implementation has to take care that the data is always updated in both places (for example by the server polling the data).
Exposing recipe information in the Address Space also allows a sophisticated client to carry out requests not covered by pre-defined methods through browsing the data on its own.
Note that sophisticated vision systems may contain a large number of recipes so that exposing the entire recipe metadata information in the Address Space may lead to a quite large Address Space.
Note, also, that this specification does not require the server to expose this information and that the client thus cannot rely on the information being present nor on it being complete as it may cover only a subset of existing recipes, e.g. the list of currently prepared recipes.