How big are your reports? How big reports needs to be? Do your reports really reflect your needs? Have they become too cluttered with data? Do you have too many reports on the same topic? How many is too many? These are the few of the questions BI developers and users should ask themselves altogether from time to time.
A report is any document with textual and/or graphical formatted output of data from one or more data sources, (previously) designed to convey a basis for decision making or operational activities. A report is characterized by the amount of data it holds (the datasets), the amount of data is based on (the source data), the number and complexity of the queries on which the report is based, the number of data sources, the manner in which data are structured (tabular, matrix, graphical), the filtering and sorting possibilities, as well by the navigability possibilities (drilldown, drill-through, slice-and-dice, etc.).
On the other side for users are important characteristics like reports’ performance, the amount of useful information it conveys, the degree to which a report helps address a business need, the quality of data, the degree to which it satisfies the various policies, the look and feel, the possibility of exporting the data to standard file formats.
A report’s size is defined typically by the product of columns and records the report displays plus the formatting and various types of graphical content, however this depends on the filter criteria used by the user. Usually is considered the average size of a report based on the typical filters used. Nowadays networks and database specific techniques allow displaying fairly big reports (20-50 Mb) in a fairly amount of time (10-20 seconds) without affecting network, respectively database’s performance, which for most of the requests should be enough. When the users need bigger volumes of data then a direct data dump (extract) from the database should be considered, when possible. (A data export is not a report and they should be differentiated as such.)
The number of records that could be shown in a report is dependent on reporting framework’s capabilities, e.g. there are reporting tools that cope well with showing a few thousands records but have difficulties in showing or exporting tens of thousands of records. The best example into this respect is Excel and its well-known limitation of 65536 records (2^16) and 256 columns (2^8) that in the meantime has been addressed in Excel 2007 and enlarged to 1 million records (2^20), respectively 16k (2^14). Even so the reporting tools that use older drivers can fail exporting all the data to Excel when the former limitation is reached.
In general, reports with too many columns tend to obfuscate data’s understanding and are more difficult to navigate. The more the user needs to scroll horizontally the higher in general the obfuscation. If the users really need 50 columns then they should be provided, however in general 20-25 should be enough for an operational report. Tactical and strategic reports need a restrained focus and the information should be provided in a screen without the need of scrolling.
When reports get too big is recommended to split the reports in two or more reports to address specific requirements, however this can lead to too many distinct reports, and further to duplication of effort for creating and documenting them, and the duplication of logic and data. Therefore, the challenge is to find the right balance between the volume of reports, their usability and the effort needed to manage them. In certain scenarios it makes even sense to consolidate similar reports.
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