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BitStream Files are a way of storing survey data in compact files. These files are optimized for fast access, to allow aggregated tables to be generated as quickly as possible for your Reportal report.
Important
The use of BitStream files is default for all new projects in Forsta Plus. However if you create a new project using the Legacy database format, BitStream files can be deselected if required. Forsta strongly recommends you use BitStream Files on all projects.
If the data source project used the Optimized database format, then BitStream files must be used. Go to the Forsta Professional Authoring documentation for further information on the Optimized database format.
It is not possible to create a report based on a Professional Panel that has no associated BitStream variants.
If a user creates a report in Version 15 Legacy format, the default option will be to use BitStream files. However if this has been deselected and you open a report for which the BitStream files have not yet been generated, then the files will be generated automatically and you will be presented with a message informing you of this. The message status will be updated when the files are available.
For Legacy projects and reports, before the BitStream Files are created for a database, when Reportal wishes to generate an aggregated table it must interrogate the SQL database directly. This can be a slow process, and it will become even slower as the database size increases. The BitStream Files are created by initiating a task in Forsta Plus that runs through the survey database and saves the survey data to files. Once the files have been created, you can go to the Properties page General tab for the report and specify the type of BitStream Files that are to be used for the current report (check the box .- see the figure below).
Note: For Forsta Plus projects (both Optimized and Legacy) you can create only two different BitStream file sets: The Rapid Results file set (which is used in Rapid Results in Express and Professional, and the Results tab/Topline report in Professional Designer), and the Reportal file set. However using Panel Management rules in Professional Panels, you can create several file sets taking different cuts of the data. Then for Panel projects in Reportal, the drop-down list will include the BitStream file sets you have created in panel rules (with the names you have assigned to them there).
Figure 1 - Selecting the BitStream variant to be used for the report
Note that for RVAs/RDAs and Forsta Plus users (not Public reports), you can add a "BitStream Updater" component to the report pages to allow the viewer to update the data displayed (go to Updating the Data on the Report Page for more information).
Differences between SQL and BitStream Results
The SQL and BitStream reporting engines produce identical results with one important exception: Handling of NULL values (missing responses) when using the NOT operator.
- In SQL, if you filter with NOT(rating="1"), the results will include all responses other than "1" (all other codes, for example codes "2", "3", "4", "5" and "DK" for don't know) but not missing responses (NULL) (where the question has not been answered at all, due to for example masking or skipping).
- When reporting based on BitStream files, the missing responses (NULL) will be included when you filter with the NOT operator.