Creating a Cognos Chart from a series of values

Hello. I am trying to create a Cognos bar chart with a series of document counts. I cant seem to get the chart made. Does the chart have to be made with related measures such as something from a cross tab or can it be made of independent data items? If it can be made, is it as simple as placing a data item with the total count in the y axis, and the individual types that need to be measured in the x axis? I have tried this previously to no avail, so any help would be highly appreciated,