Each Qlikview document can have only one data model. First you should be preparing your holistic data model by first extracting data from Oracle and/or SQL database and then associating your data through script based on business needs or requirement.
Once you are ready with your data model, you will understand how different fields should get associated with each other in front end through charts.
I totally agreed with you about having a holistic view of the data model. This QV app was created by someone and I'm new to QV development. I was trying to see if there was an easier way for me to pull this one number out of the SQLChart and use it in my OracleChart. One thing I can probably do is somehow setup a formula and stick the result in variable. Then reference this variable in the chart where I need to the math.