Tuesday, September 25, 2007

question and answers in bw

BW Questions-PART-I

1. What is the difference between OLTP and OLAP?
OLTP Current data Short database transactions Online update/insert/delete Normalization is promoted High volume transactions Transaction recovery is necessary

OLAP Current and historical data Long database transactions Batch update/insert/delete Renormalization is promoted Low volume transactions Transaction recovery is not necessary

OLTP is nothing but OnLine Transaction Processing ,which contains a normalised tables and online data,which have frequent insert/updates/delete.
But OLAP(Online Analtical Programming) contains the history of OLTP data, which is, non-volatile ,acts as a Decisions Support System and is used for creating forecasting reports.

2. What is different type of multidimensional models?

3. What is the dimension?.

A grouping of those evaluation groups (characteristics) that belong together under a common superordinate term.
With the definition of an InfoCube, characteristics are grouped together into dimensions in order to store them in a star schema table (dimension table).

4. What is the fact and fact table?
Table in the center of an InfoCube star schema.
The data part contains all key figures of the InfoCube and the key is formed by links to the entries of the dimensions of the InfoCube.

5. Difference between key performance indicators (KPI) and key figures?.

Key Performance Indicators are quantifiable measurements, agreed to beforehand, that reflect the critical success factors of an organization. They will differ depending on the organization. A business may have as one of its Key Performance Indicators the percentage of its income that comes from return customers. A school may focus its Key Performance Indicators on graduation rates of its students. A Customer Service Department may have as one of its Key Performance Indicators, in line with overall company KPIs, percentage of customer calls answered in the first minute. A Key Performance Indicators for a social service organization might be number of clients assisted during the year.
Whatever Key Performance Indicators are selected, they must reflect the organization's goals, they must be key to its success,and they must be quantifiable (measurable). Key Performance Indicators usually are long-term considerations. The definition of what they are and how they are measured do not change often. The goals for a particular Key Performance Indicator may change as the organizations goals change, or as it get closer to achieving a goal.
. 6. Difference between star schema and Extended star schema?

The difference between star and extended star schemas:1) Master data is not reusable in STAR because it is inside a cube. i.e in star scheme Dimensional tables and Master data tables are same. these 2 are inside a cube. But in extended star shema master data tables are outside the cube. so these are reusable components. here master data tables and Dimensional tables are different.2) limited Analysis: in star schema the maximum number of master data tables are 16. But in extended star schema the maximum number of Dimensioanl tables are 16. we can assign maximum of 233 char to one dimensional table. in that way we can assign 233*16 Char.3) low performance: in star schema it is used ALPHA numeric data. in Extended star schema we are using numering data. like we are generating SID inorder to link with dimesional tables these are numeric data. so performance is low regarding star schema.

7.what is a dimension table in extended star schema and when it is exactly created and when it will get populated?.

8. What is a SID (Surrogate ID) table in extended star schema and when it is exactly created and when it will get populated?.

9. what are the limitation techniques of infocube or modeling in BW?.

10. what is Flexiable update and Direct Update and explain difference?.
When we load data to the data target at the level of info provider level then we go for flexible update (wheither it is M.D or T.D). When we load data to the data target at the level of Info Object we go for Direct update.

Main Deference is Direct updata = without Update rulesFlexible update= With update rules
Scenarios for Flexible Updating
1. Attributes and texts are delivered together in a file:
Your master data, attributes, and texts are available together in a flat file. They are updated by an InfoSource with flexible updating in additional InfoObjects. In doing so, texts and attributes can be separated from each other in the communication structure.
Flexible updating is not necessary if:
· texts and attributes are available in separate files/DataSources. In this case, you can choose direct updating if additional transformations using update rules are not necessary.
2. Attributes and texts come from several DataSources:
This scenario is similar to the one described above, only slightly more complex. Your master data comes from two different source systems and delivers attributes and texts in flat files. They are grouped together in an InfoSource with flexible updating. Attributes and texts can be separated in the communication structure and are updated further in InfoObjects. The texts or attributes from both source systems are located in these InfoObjects.
3. Master data in the ODS layer:
A master data InfoSource is updated to a master data ODS object business partner with flexible updating. The data can now be cleaned and consolidated in the ODS object before being re-read. This is important when the master data frequently changes.
These cleaned objects can now be updated to further ODS Objects. The data can also be selectively updated using routines in the update rules. This enables you to get views of selected areas. The data for the business partner is divided into customer and vendor here.
Instead you can update the data from the ODS object in InfoObjects as well (with attributes or texts). When doing this, be aware that loading of deltas takes place serially. You can ensure this when you activate the automatic updates in ODS object maintenance or when you perform the loading process using a process chain (see also Including ODS Objects in a Process Chain).
A master data ODS object generally makes the following options available:
· It displays an additional level on which master data from the whole enterprise can be consolidated.
· ODS objects can be used as a validation table for checking the referential integrity of characteristic valuables in the update rules.
· It can serve as a central repository for master data, in which master data is consolidated from various systems. They can then be forwarded to further BW systems using the Data Mart.

Direct update is generally used for Master data infoobject & Hoerarchies . Here no update rules are used, that means data from source system passes though transfer structure, rules, & communication structure directly to Data target i.e. InfoObject.

11. what are transfer rules and updates rules and difference?.
Why we are using update rule while loading the data from source syst?Why can not we directly load data from transfer rule to datatarget..?Update rules are after the infosource and before the data target. Transactional Data can not be loaded into the data target without passing through the update rules.Incase of master data Update rules are not required.Let us take one example. Say you have Customer quantity price revenue and date.you have the data cust, Qty, Prc and date extracted from Source system. Assume that you can not Extract Rev.In transfer rules you can apply some rules on Qty and Prc and Rev can be derived.Suppose if requirement is period also should be presented in the report.Then in the update rules by setting date in the time Ref char, sytem will give the period, week, month ets like values.Like wise depending upon the requirements you can use the update rules.These rules to be applied to fill the data target.As per the these rules data sits in the respective object locations.
The reason for having update rules would be:1. If a business logic lets say if a certain quantity > '5' - then rating is "A" needs to be implemented you would have to do it in all the transfer rules whereas in a update rule only once.2. You can use return tables in update rules which would split the incoming data package record into multiple ones. This is not possible in transfer rules. 3. Currency conversion is not possible in transfer rules.4. If you have a key figure that is a calculated one using the base key figures you would do the calculation only in the update rules.
4 types:1) InfoObject: Direct mapping2) Constants: A fixed value. 3) Formula: value is determined using a formula.4) Routine: ABAP programs

12. what is the update mode , update method update type for updating data into infocube?.

13. what is the PSA and advantages and disadvantages of PSA ?.

14. what are the fields of PSA?.

15.how many data sources can be assigned to in infosource?.

16. what are different transformation methods in transfer rules.?.

15. What is ER Diagram

The Entity-Relationship (ER) model was originally proposed by Peter in 1976 [Chen76] as a way to unify the network and relational database views. Simply stated the ER model is a conceptual data model that views the real world as entities and relationships. A basic component of the model is the Entity-Relationship diagram which is used to visually represents data objects. Since Chen wrote his paper the model has been extended and today it is commonly used for database design For the database designer, the utility of the ER model is: it maps well to the relational model. The constructs used in the ER model can easily be transformed into relational tables. it is simple and easy to understand with a minimum of training. Therefore, the model can be used by the database designer to communicate the design to the end user. In addition, the model can be used as a design plan by the database developer to implement a data model in a specific database management software.

why an infocube has maximum of 16 dimensions?
As the total charecterstics are 255, out of which 16 charecters are being allowed for foreign keys and 6 charecters are for sap default, for this sake we have only 16 dimention tables, of which 3 are again sap default (unit, time. Datapacket): so finally we have only 13 user dimentions.

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