Thursday, December 17, 2015

Conquering Basics:Part 02 Persistent Staging Area and Infoobjects

  Before moving on to loading issues, we will first quickly introduce you to SAP objects used in numerous staging layers. A Comprehensive description of these objects can be found in the official SAP website and I wont repeat them here. But I will explain it to you in my way, with real world examples.

Persistent Staging Area
The PSA(Persistent Staging Area) is the entry point into the BW system.Data from the source system(ECC) first arrives here where we cleanse it according to certain rules(no special characters allowed, no capital letters allowed etc). We edit these records for it to be ready to be sent to the reporting layers. Of the ETL, Extraction happens in this stage and to some extent the transformation.A Transfer structure represents a 1:1 mapping between source and BW system using which data is transferred from source(where users post) to BW. For each data source in the ECC, the same DS is created in BW which contains a transparent table(PSA). A transparent table is the one whose definition is as a single and independent table in database. SAP also has pooled table and cluster tables.

Example: A company keeping an employee in probation period is as good as data being stored in the PSA. Being in the probation period is not the final fate of an employee, either he is made permanent or he is removed from the company.Similarly, each data record in the PSA is either transferred to the subsequent reporting layers or is discarded. An employee in probation doesn't enjoy those rights given to a permanent employee in the same way as any record in the PSA cannot be used for reporting unless transferred ahead.

An Infobject is a business evaluation object which is itself responsible for distributing and dividing data logically.An infoobject contains characteristics(company code,fiscal year period,region),key figures(amount,number,quantity) etc. These are reflected in multidimensional cubes whilst reporting. If the characteristics have Text, Attributes and Hierarchies as its part then the info object is sure to contain Master data.WHY?
Consider the below example determine whether a transnational data can have attributes,texts and hierarchies.
Example: Suppose I load employee master data. Here MD attributes will be employee name,employee number etc. The  details to these attributes are stored in MD Texts. Hierarchies are nothing but an organisational structure according to which data is classified. A hierarchy can be considered similar to the following flow( Organisation-->Continental Level branches-->Country wise branches-->Region wise brahcnes in a country).
Note: Hierarchies play a very important role in roll up and drill down operations in BW reporting. Rollup and Drill down are the unique features owing to which many organisations opt for a BI system.

Lets continue the basics in the upcoming article.