Data Islands are group of unassociated data tables. In qlikview it is not that always every table in your data model will contribute to form a Star Schema. There might be few tables which are not associated to any other tables in the Data Model and the data from these tables will be used in your Dashboard for reporting purposes.
One of the simplest scenarios is this (it's really simple, never mind the number of words I need to explain it):
Imagine you want to be able to decide which expressions should be shown in a (large) straight table, simply by selecting them from a listbox on the left side or at the top in your document. A table that you can customise by selecting stuff in the AccessPoint, and not by reprogramming the object in QV Desktop.
For that to happen, you first create an INLINE table in your script that contains one field with expression labels. This table has no connection to any other table (= Date/Data Island). On the sheet of the straight table, you add a listbox that shows the values from this field. Selecting any or all values will not do anything with the other objects or rows because there is no associative link to anything else in the data model.
Next, in your straight table you add expressions for each of the labels in the listbox. For each expression, you enable the Condition Show and add a conditional show expression that tests the listbox selections for a particular label (use the GetCurrentSelections() and WildMatch() functions to do that). If the label is selected, the expression will appear in the table, otherwise it will be hidden.
