MII Trends - add data onto chart object

Question

Hello,
Can anyone please provide some thoughts on my current requirement:
its pretty basic:
I select a site(Historian datasource) search for a historian tag and then based on the selection I Trend(lets say Line chart).
Now I should select another site(historian datasource) search for a historian tag and add the tag onto the line chart along with the previous one.
so basically give user an option to select any historian data source and trend.
While i do this, i should still be able to use the in built chart properties mainly the time control - to go back and forht in time..
while I am doing this, I am also keeping a running list of selected tags in another table with the tag's other properties -like current value, Eng Units, calculation, Description, datasource.and give an option with a check box to this running list - where in user can check /uncheck the item and that removes the pen from the chart - and maintaining the chart pen color consistent with the running list's item's color(check box color - for ease of matching) - I am able to accomplish this part successfully.
I grealty appreciate if any one cane give me some ideas.on how to adynamically add tags onto the chart from multiple datasources and maintian the inbuilt properties of the line chart.
As you can see, I am almost building a product here - similar to Aspen's web21 or osi's process explorer - using MII.
any input is greatly appreciated.
Regards,
pramod

Answer 1

The built-in features of the iChart allow the basic premise of what you are trying to do, however it limits you to one Data Server at a time in the iChart, because a single query template only has one data server source, but with an XacuteConnector as your data source you can do whatever you need.
You'll need to keep track of their choices either in an array or string list so you can appropriately bind it to the Param.x in your underlying Xacute Query template.  The BLS logic for running the queries, and overloading the Server and Tags will be up to you.
The start and end date mapping for your Xacute query template will make the chart work like a typical Historian line trend with time controls. You'll just need to create the date inputs (DateTime datatype in your Transaction property) and link to the QueryStartDate/QueryEndDate of each tag query action.
You don't need to merge the data into one rowset. The chart will be happy with 1 Rowset per tag like you see from either Current, History, or HistoryEvent from a real Historian (not like Simulator's merged normalized dataset).  You may just want to consider creating the Transaction OutputXML, and use the AssignXML for the first data source query, followed by AppendXML for just the Rowset(s) from each subsequent data source query.  This way you keep building into the OutputXML in your loop.