DWH Concepts FAQs1

7/30/2019 DWH Concepts FAQs1

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Data warehousing concepts (FAQs)

1) What is Data warehouse?

Data warehouse is relational database used for query analysis and

reporting. By definition data warehouse is Subject-oriented, Integrated,

Non-volatile, Time variant.

Subject oriented : Data warehouse is maintained particular subject.

Integrated : Data collected from multiple sources integrated into a

user readable unique format.

Non volatile : Maintain Historical date.

Time variant : data display the weekly, monthly, yearly.

2) What is Data mart?

A subset of data warehouse is called Data mart.

3) Difference between Data warehouse and Data mart?

Data warehouse is maintaining the total organization of data. Multiple

data marts used in data warehouse. where as data mart is maintained only

particular subject.

4) Difference between OLTP and OLAP?

OLTP is Online Transaction Processing. This is maintained current

transactional data. That means insert, update and delete must be fast.

5) Explain ODS?

Operational data store is a part of data warehouse. This is maintained only

current transactional data. ODS is subject oriented, integrated, volatile,

current data.

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6) Difference between Power Center and Power Mart?

Power center receive all product functionality including ability to multiple

register servers and metadata across the repository and partition data.

One repository multiple informatica servers. Power mart received allfeatures except multiple register servers and partition data.

7) What is a staging area?

Staging area is a temporary storage area used for transaction, integrated

and rather than transaction processing.

When ever your data put in data warehouse you need to clean and

process your data.

8) Explain Additive, Semi-additive, Non-additive facts?

Additive fact: Additive Fact can be aggregated by simple

arithmetical additions.

Semi-Additive fact: semi additive fact can be aggregated simple

arithmetical

additions along with some other dimensions.

Non-additive fact: Non-additive fact cant be added at all.

9) What is a Fact less Fact and example?

Fact table which has no measures.

10) Explain Surrogate Key?

Surrogate Key is a series of sequential numbers assigned to be a primary

key for the table.

11) How many types of approaches in DHW?

Two approaches: Top-down(Inmol approach), Bottom-up(Ralph

Kimball)

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12) Explain Star Schema?

Star Schema consists of one or more fact table and one or more

dimension tables that are related to foreign keys.

Dimension tables are De-normalized, Fact table-normalized

Advantages: Less database space & Simplify queries.

13) Explain Snowflake schema?

Snow flake schema is a normalize dimensions to eliminate the

redundancy.The dimension data has been grouped into one large table.

Both dimension and fact tables normalized.

14) What is confirm dimension?

If both data marts use same type of dimension that is called confirm

dimension.If you have same type of dimension can be used in multiple

fact that is called confirm dimension.

15) Explain the DWH architecture?

16) What is a slowly growing dimension?

Slowly growing dimensions are dimensional data,there dimensions

increasing dimension data with out update existing dimensions.That

means appending new data to existing dimensions.

17) What is a slowly changing dimension?

Slowly changing dimension are dimension data,these dimensions

increasing dimensions data with update existing dimensions.

Type1: Rows containing changes to existing dimensional are update in the

target by overwriting the existing dimension.In the Type1 Dimension

mapping, all rows contain current dimension data.

Use the type1 dimension mapping to update a slowly changing

dimension table when you do not need to keep any previous versions of

dimensions in the table.

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Type2: The Type2 Dimension data mapping inserts both new and changed

dimensions into the target.Changes are tracked in the target table by

versioning the primary key and creating a version number for each

dimension in the table.

Use the Type2 Dimension/version data mapping to update a slowly

changing dimension when you want to keep a full history of dimension

data in the table.version numbers and versioned primary keys track the

order of changes to each dimension.

Type3: The type 3 dimension mapping filters source rows based on user-

defined comparisions and inserts only those found to be new dimensions

to the target.Rows containing changes to existing dimensions are updated

in the target. When updating an existing dimension the informatica server

saves existing data in different columns of the same row and replaces theexisting data with the updates.

18) When you use for dynamic cache?

Your target table is also look up table then you go for dynamic cache .In

dynamic cache multiple matches return an error.use only = operator.

19) what is lookup override?

Override the default SQL statement.You can join multiple sources uselookup override.By default informatica server add the order by clause.

20) Can we pass the null value in lookup transformation?

Lookup transformation returns the null value or equal to null value.

21) what is the target load order?

You specify the target load order based on source qualifiers in a

mapping.if u have the multiple source qualifiers connected to the multipletargets you can designate the order in which informatica server loads data

into the targets.

22) what is default join that source qualifier provides?

Inner equi join.

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23) what are the difference between joiner transformation and source

qualifier transformation?

You can join heterogeneous data sources in joiner transformation, which

we cannot achive in source qualifier transformation.

You need matching keys to join two relational sources in source qualifier

transformation.where you doesnt need matching keys to join two sources.

Two relational sources should come from same data source in source

qualifier.You can join relational sources, which are coming from different

sources in source qualifier.You can join relational sources which are

coming from different sources also.

24) what is update strategy transformation?

Whenever you create the target table whether you are store the historical

data or current transaction data in to target table.

25) Describe two levels in which update strategy transformation sets?

26) what is default source option for update strategy transformation?

Data driven.

27) What is data driven?

The information server follows instructions coded into update strategy

transformations with in the session mapping determine how to flag

records for insert,update,delete or reject if u do not choose data driven

option setting , the informatica server ignores all update strategy

transformations in the mapping.

28) what are the options in the trarget session of update strategy

transformation?

Insert

Delete

Update

Update as update

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Update as insert

Update else insert

Truncate table.

29) Difference between the source filter and filter?

Source filter is filtering the data only relational sources. Where as filter

transformation filter the data any type of source.

30) what is a tracing level?

Amount of information sent to log file.

-- What are the types of tracing levels?

Normal,Terse,verbose data,verbose intitialization.

--Expalin sequence generator transformation?

--can you connect multiple ports from one group to multiple

transformations?

Yes

31) can you connect more than one group to the same target or

transformation?

NO

32) what is a reusable transformation?

Reusable transformation can be a single transformation.This

transformation can be used in multiple mappings.when you need to

incorporate this transformation into mapping you add an instance of it tomapping.Later if you change the definition of the transformation, all

instances of it inherit the changes.Since the instance of reusable

transformation is a pointer to that transformation.U can change the

transformation in the transformation developer, its instance automatically

reflect these changes. This feature can save U great deal of work.

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-- what are the methods for creating reusable transformation?

Two methods

1) Design it in the transformation developer.

2) Promote a standard transformation from the mappingdesigner.After you add a transformation to the mapping, you can promote

it to status of reusable transformation.

Once you promote a standard transformation to reusable status, you can

demote it to a standard transformation at any time.

If u change the properties of a reusable transformation in mapping , you

can revert it to the original reusable transformation properties by clicking

the revert.

33) what are mapping parameters and mapping variables?

Mapping parameter represents a constant value that you can define before

running a session.A mapping parameter retains the same value throughout

the entire session.

When you use the mapping parameter , you declare and use the parameter

in a mapping or mapplet.Then define the value of parameter in a

parameter file for the session.

Unlike a mapping parameter, a mapping variable represents a value that

can change through out the session. The informatica server save the value

of mapping variable to the repository at the end of session run and uses

that value next time you run the session.

34) can you use the mapping parameters or variables created in one

mapping into another mapping?

NO, we can use mapping parameters or variables in any transformation ofthe same mapping or mapplet in which have crated mapping parameters

or variables.

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35) Can you are the mapping parameters or variables created in one

mapping into any other result transformation?

Yes because the reusable transformation is not contained with any

mapplet or mapping.

36) How the informatica server sorts the string values in rank

transformation?

When the informatica server runs in the ASCII data movement mode it

sorts session data using binary sort order.If you configures the session to

use a binary sort order, the informatica server calculates the binary value

of each string and returns the specified number of rows with the highest

binary values for the string.

37) What is the rank index in rank transformation?

The designer automatically creates a RANKINDEX port for each Rank

transformation. The informatica server uses the Rank Index port to store

the ranking position for each record in a group.For example, if you create

a Rank transformation that ranks the top 5 sales persons for each quarter,

the rank index number the salespeople from 1 to 5.

38) what is the mapplet?

Mapplet is a set of transformation that you build in the mapplet designer

and you can use in multiple mappings.

39) Difference between mapplet and reusable transformation?

Reusable transformation can be a single transformation.Where as mapplet

use multiple transformations.

40) what is a parameter a file?

Paramater file defines the values for parameter and variables.

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WORKFLOW MANAGER

41) what is a server?

The power center server moves data from source to targets based on a

workflow and mapping metadata stored in a repository.

42) what is a work flow?

A workflow is a set of instructions that describe how and when to run

tasks related to extracting,transformation and loading data.

-- what is session?

A session is a set of instructions that describes how to move data from

source to target using a mapping.

-- what is workflow monitor?

Use the work flow monitor work flows and stop the power center server.

43) explain a work flow process?

The power center server uses both process memory and system shared

memory to perform these tasks.

Load manager process: stores and locks the workflow tasks and start the

DTM run the sessions.

Data Transformation Process DTM: Perform session validations,create

threads to initialize the session,read,write and transform data, and handle

pre and post session operations.

The default memory allocation is 12,000,000 bytes.

44) What are types of threads in DTM?

The main dtm thread is called the master thread.

Mapping thread.

Transformation thread.

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Reader thread.

Writer thread.

Pre-and-post session thread.

45) Explain work flow manager tools?

Task developer.

Work flow designer.

Worklet designer.

46) Explain work flow schedule.

You can sehedule a work flow to run continuously, repeat at given time or

interval or you manually start a work flow.By default the workflow runs

on demand.

47) Explain stopping or aborting a session task?

If the power center is executing a session task when you issue the stop the

command the power center stop reading data. If continuous processing

and writing data and committing data to targets.

If the power center cant finish processing and committing data you issue

the abort command.

You can also abort a session by using the Abort() function in the mapping

logic.

48) What is a worklet?

A worklet is an object that represents a set of tasks.It can contain any task

available in the work flow manager. You can run worklets inside a

workflow. You can also nest a worklet in another worklet.The worklet

manager does not provide a parameter file for worklets.

The power center server writes information about worklet execution in the

workflow log.

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49) what is a commit interval and explain the types?

A commit interval is the interval at which power center server commits

data to targets during a session. The commit interval the number of rows

you want to use as a basis for the commit point.

Target Based commit: The power center server commits data based on the

number of target rows and the key constraints on the target table. The

commit point also depends on the buffer block size and the commit

interval.

Source-based commit:---------------------------------------------

User-defined commit:----------------------------------------------

50) Explain bulk loading?

You can use bulk loading to improve performance of a session that inserts

a large amount of data to a db2,sysbase,oracle or MS SQL server

database.

When bulk loading the power center server by passes the database

log,which speeds performance.

With out writing to the database log, however the target database cant

perform rollback.As a result you may not be perform recovery.

51) What is a constraint based loading?

When you select this option the power center server orders the target load

on a row-by-row basis only.

Edit tasks->properties->select treat source rows as insert.

Edit tasks->config object tab->select constraint based

If session is configured constraint absed loading when target table receive

rows from different sources.The power center server revert the normal

loading for those tables but loads all other targets in the session using

constraint based loading when possible loading the primary key table first

then the foreign key table.

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Use the constraint based loading only when the session option treat rows

as set to insert.

Constraint based load ordering functionality which allows developers to

read the source once and populate parent and child tables in a single

process.

52) Explain incremental aggregation?

When using incremental aggregation you apply captured changes in the

source to aggregate calculations in a session.If the source changes only

incrementally and you can capture changes you can configure the session

to process only those changes. This allows the power center server to

update your target incrementally rather than forcing it to process the entire

source and recalculate the same data each time you run the session.

You can capture new source data.use incremental aggregation when you

can capture new source data much time you run the session.Use a stored

procedure on filter transformation only new data.

Incremental changes do not significantly change the target.Use

incremental aggregation when the changes do not significantly change the

target.If processing the incrementally changed source alters more than

half the existing target, the session may not benefit from using

incremental aggregation. In this case drop the table and recreate the targetwith complete source data.

53) Processing of incremental aggregation

The first time u run an incremental aggregation session the power center

server process the entire source.At the end of the session the power center

server stores aggregate data from the session runs in two files, the index

file and the data file .The power center server creates the files in a local

directory.

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Transformations.

--- what is transformation?

Transformation is repository object that generates modifies or passes data.

54) what are the type of transformations?

2 types:

1) active

2) passive.

-- explain active and passive transformation?

Active transformation can change the number of rows that pass

through it.No of output rows less than or equal to no of input rows.

Passive transformation does not change the number of rows.Always

no of output rows equal to no of input rows.

55) Difference b/n filter and router transformation.

Filter transformation to filter the data only one condition and drop the

rows dont meet the condition.

Drop rows does not store any ware like session log file..

Router transformation to filter the data based on multiple conditions and

give you the option to route rows that dont match to a default group.

56) what r the types of groups in router transformation?

Router transformation 2 groups 1. Input group 2. output groups.

Output groups in 2 types. 1. user defined group 2. default group.

57) difference between expression and aggregator transformation?

Expression transformation calculate the single row values before writes

the target.Expression transformation executed by row-by-row basis only.

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Aggregator transformation allows you to perform aggregate calculations

like max, min,avg

Aggregate transformation perform calculation on groups.

58) How can u improve the session performance in aggregatetransformation?

Use stored input.

59) what is aggregate cache in aggregate transformation?

The aggregate stores data in the aggregate cache until it completes

aggregate calculations.When u run a session that uses an aggregate

transformation , the informatica server creates index and data caches in

memory is process the transformation. If the informatica server requires

more space it stores overview values in cache files.

60) explain joiner transformation?

Joiner transformation joins two related heterogeneous sources residing in

different locations or files.

--What are the types of joins in joiner in the joiner transformation?

Normal

Master outer

Detail outer

Full outer

61) Difference between connected and unconnected transformations?

Connected transformation is connected to another transformation with in amapping.

Unconnected transformation is not connected to any transformation with

in a mapping.

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62) In which conditions we cannot use joiner transformation(limitations

of joiner transformation)?

Both pipelines begin with the same original data source.

Both input pipelines originate from the same source qualifiertransformation.

Both input pipelines originate from the same normalizer

transformation

Both input pipelines originate from the same joiner transformation.

Either input pipelines contains an update strategy transformation

Either input pipelines contains sequence generator transformation.

63) what are the settings that u use to configure the joiner

transformation?

Master and detail source.

Type of join

Condition of the join

64) what is look up transformation

look up transformation can be used in a table view based on condition by

default lookup is left outer join

65) why use the lookup transformation?

To perform the following tasks.

Get a related value.For example if your table includes employee ID,but

you want to include such as gross sales per invoice or sales tax but not the

calculated value(such as net sales)

Update slowly changing dimension tables. You can use a lookup

transformation to determine whether records already exist in the target.

66) what are the types of lookup?

Connected and unconnected

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67) difference between connected and unconnected lookup?

Connected lookup Unconnected lookup

Receives input values

directly from the pipe

line.

Receives input values from the result of a clkp

expression in a another transformation.

U can use a dynamic

or static

Cache

U can use a static cache

Cache includes all

lokkup columns used

in the mapping(that is

lookup table columns

included in the lookupcondition and lookup

table columns linked

as output ports to

other transformations)

Cache includes all lookup/output ports in the

lookup condition and the lookup/return port.

Can return multiple

columns from the

same row or insert

into the dynamic

lookup cache.

Designate one return port(R).Returns one

column from each row.

If there is no match

for the lookup

condition, the

informatica server

returns the default

value for all output

ports.If u configure

dynamic caching the

informatica server

inserts rows into thecache.

If there is no matching for the lookup

condition the informatica server returns NULL

Pass multiple output

values to another

transformatnion.Link

lookup/output ports to

another

Pass one output value to another

transformation.The lookup/output/return port

passes the same value to the

---------------------------------------------------------

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transformation

Supports user-defined

default values.

Does not support user-defined default values.

68) explain index cache and data cache?

The informatica server stores conditions values in the index cache and

output values in the data cache.

69) What are the types of lookup cache?

Persistent cache: U can save the look up cache files and reuse them

the next time the informatica server processes a lookup

transformation to use the cache.

Static cache: U can configure a static or read-only lookup table.By

default informatica server creates a static cache.It caches the lookup

table and lookup values in the cache for each row that comes into

the transformation.When the lookup condition is true the

inforamtica server does not update the cache while it processes the

lookup transformation.

Dynamic cache: If you want to cache the target table and insert new

rows into cache and the target you can create a look uptransformation to use dynamic cache.The informatica server

dynamically inserts data into the target table.

Shared cache: You can share the lookup cache between multiple

transformations.You can share unnamed cache between

transformation in the same mapping.

70) Difference between static cache and dynamic cache?

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Static cache Dynamic cache

You cannot insert or

update the cache

You can insert rows into the

cache as you pass rows to the

target

The informatica serverreturns a value from

the lookup table or

cache when the

condition is true,.When

the condition is true the

informatica server

returns the default

value for connected

transformation

The informatica server insertsrows into the cache when the

condition is false.This indicates

that the row in the cache or

target table.You can pass these

rows to the target table.

ORACLE:

71) Difference between primary key and unique key?

Primary key is Not null unique

Unique accept the null values.

72) Difference between inserting and sub string?

73) What is referential integrity?74) Difference between view and materialized view?

75) What is Redolog file?

The set of redo log files for a database is collectively know as the

databases redo log.

76) What is RollBack statement?

A database contains one or more rollback segments to temporarily store

undo information.Roll back segment are used to generate read consistantdata base information during database recovery to rooback uncommitted

transactions for users.

-- what is table space?

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A data base is divided into logical storage unit called table space.A table

space is used to grouped related logical structures together.

-- How to delete the duplicate records.

-- What are the difference types of joins in Oracle?

Self-join,equi-join,outer join.

77) What is outer join?

One of which rows that dont match those in the commen column of

another table.

78) write query Max 5 salaries?

Select * from emp e where 5>(select count(*) from emp where sal>e.sal)

79) what is synonym?

80) --------------------------------

81)82) What is bit map index and example?

83) What is stored procedure and advantages?

84) Explain cursor and how many types of triggers in oracle?

Trigger is stored procedure.Trigger is automatically executed.

85) Difference between function and stored procedure?

Function returns a value.Procedure does not return a value(but returns a

value tru IN OUT parameters!!!!!!)

86) Difference between replace and translate?

87) Write the query nth max sal

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Select distinct (a.sal) from emp a where &n=select count(distinct(b.sal)

from emp b where a.sal

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DWH Concepts FAQs1