What is the difference between a data warehouse and a data mart

Download What is the difference between a data warehouse and a data mart

Post on 08-Apr-2018




0 download

Embed Size (px)


<ul><li><p>8/7/2019 What is the difference between a data warehouse and a data mart</p><p> 1/5</p><p>What is the difference between a data warehouse and a</p><p>data mart?</p><p>This is a heavily debated issue. There are inherent similarities between the basic constructs usedto design a data warehouse and a data mart. In general a Data Warehouse is used on an</p><p>enterprise level, while Data Marts is used on a business division/department level. A data martonly contains the required subject specific data for local analysis.Back to top of file</p><p>What is the difference between a W/H and an OLTP</p><p>application?</p><p>Typical relational databases are designed for on-line transactional processing (OLTP) and do notmeet the requirements for effective on-line analytical processing (OLAP). As a result, datawarehouses are designed differently than traditional relational databases.</p><p>Warehouses are Time Referenced, Subject-Oriented, Non-volatile (read only) and Integrated.</p><p>OLTP databases are designed to maintain atomicity, consistency and integrity (the "ACID" tests).Since a data warehouse is not updated, these constraints are relaxed.</p><p> Back to top of file</p><p>What is the difference between OLAP, ROLAP, MOLAP</p><p>and HOLAP?</p><p>ROLAP, MOLAP and HOLAP are specialized OLAP (Online Analytical Analysis) applications.</p><p>ROLAP stands for Relational OLAP. Users see their data organized in cubes with dimensions,but the data is really stored in a Relational Database (RDBMS) like Oracle. The RDBMS will storedata at a fine grain level, response times are usually slow.</p><p>MOLAP stands for Multidimensional OLAP. Users see their data organized in cubes withdimensions, but the data is store in a Multi-dimensional database (MDBMS) like Oracle ExpressServer. In a MOLAP system lot of queries have a finite answer and performance is usually criticaland fast.</p><p>HOLAP stands for Hybrid OLAP, it is a combination of both worlds. Seagate Software's Holos isan example HOLAP environment. In a HOLAP system one will find queries on aggregated data</p><p>as well as on detailed data.</p><p> Back to top of file</p><p>What is the difference between an ODS and a W/H?</p>http://www.orafaq.com/faqwh.htm#TopOfFile%23TopOfFilehttp://www.orafaq.com/faqwh.htm#TopOfFile%23TopOfFilehttp://www.orafaq.com/faqwh.htm#TopOfFile%23TopOfFilehttp://www.seagatesoftware.com/http://www.orafaq.com/faqwh.htm#TopOfFile%23TopOfFilehttp://www.orafaq.com/faqwh.htm#TopOfFile%23TopOfFilehttp://www.seagatesoftware.com/http://www.orafaq.com/faqwh.htm#TopOfFile%23TopOfFilehttp://www.orafaq.com/faqwh.htm#TopOfFile%23TopOfFile</li><li><p>8/7/2019 What is the difference between a data warehouse and a data mart</p><p> 2/5</p><p>An ODS (Operational Data Store) is an integrated database of operational data. Its sourcesinclude legacy systems and it contains current or near term data. An ODS may contain 30 to 90days of information.</p><p>A warehouse typically contains years of data (Time Referenced). Data warehouses group data bysubject rather than by activity (subject-oriented). Other properties are: Non-volatile (read only)</p><p>and Integrated.</p><p> Back to top of file</p><p>What is the difference between Oracle Express and</p><p>Oracle Discoverer?</p><p>Express is an MD database and development environment. Discoverer is an ad-hoc end-userquery tool.</p><p>Back to top of file</p><p>Q. Why should the OLTP database different from data warehouse database?</p><p> OLTP and data warehousing require two very differently configured systems</p><p> Isolation of Production System from Business Intelligence System</p><p> Significant and highly variable resource demands of the data warehouse</p><p> Cost of disk space no longer a concern</p><p> Production systems not designed for query processing</p><p>Data warehouse usually contains historical data that is derived from transaction data, but it can</p><p>include data from other sources. Having separate databases will separate analysis workload fromtransaction workload and enables an organization to consolidate data from several sources.</p><p>Q. What is the main difference between Data Warehousing and Business Intelligence?</p><p>The differentials are:</p><p>DW - is a way of storing data and creating information through leveraging data marts. DM's aresegments or categories of information and/or data that are grouped together to provide'information' into that segment or category. DW does not require BI to work. Reporting tools cangenerate reports from the DW.</p><p>BI - is the leveraging of DW to help make business decisions and recommendations. Information</p><p>and data rules engines are leveraged here to help make these decisions along with statisticalanalysis tools and data mining tools.</p><p>Q. What is the difference between OLTP and OLAP?</p><p>OLAP - Online Analytical processing, mainly required for DSS, data is in denormalized mannerand mainly used for non volatile data, highly indexed, improve query response time</p>http://www.orafaq.com/faqwh.htm#TopOfFile%23TopOfFilehttp://www.orafaq.com/faqwh.htm#TopOfFile%23TopOfFilehttp://www.orafaq.com/faqwh.htm#TopOfFile%23TopOfFilehttp://www.orafaq.com/faqwh.htm#TopOfFile%23TopOfFile</li><li><p>8/7/2019 What is the difference between a data warehouse and a data mart</p><p> 3/5</p><p>OLTP - Transactional Processing - DML, highly normalized to reduce deadlock &amp; increaseconcurrency</p><p>Q. What is the difference between OLTP and data warehouse?</p><p>Operational System Data Warehouse</p><p>Transaction Processing Query ProcessingTime Sensitive History Oriented</p><p>Operator View Managerial View</p><p>Organized by transactions (Order,Input, Inventory)</p><p>Organized by subject (Customer,Product)</p><p>Relatively smaller database Large database size</p><p>Many concurrent users Relatively few concurrent users</p><p>Volatile Data Non Volatile Data</p><p>Stores all data Stores relevant data</p><p>Not FlexibleFlexible</p><p>What is the difference between sequential file and a dataset? When to usethe copy stage?</p><p>Sequentiial Stage stores small amount of the data with any extension in order to</p><p>acces the file where as DataSet is used to store Huge amount of the data and itopens only with an extension (.ds ) .The Copy stage copies a single input data set to</p><p>a number of output datasets. Each record of the input data set is copied to everyoutput data set.Records can be copied without modification or you can drop or</p><p>change theorder of columns.</p><p>What is the exact difference betwwen Join,Merge and Lookup Stage??</p><p>The exact difference between Join,Merge and lookup is</p><p>The three stages differ mainly in the memory they use</p><p>DataStage doesn't know how large your data is, so cannot make an informed choice</p><p>whether to combine data using a join stage or a lookup stage. Here's how to decidewhich to use:</p><p>if the reference datasets are big enough to cause trouble, use a join. A join does a</p><p>high-speed sort on the driving and reference datasets. This can involve I/O if thedata is big enough, but the I/O is all highly optimized and sequential. Once the sort</p><p>is over the join processing is very fast and never involves paging or other I/O</p><p>Unlike Join stages and Lookup stages, the Merge stage allows you to specify severalreject links as many as input links.</p><p>What is the difference between Datastage and Datastage TX?Its a critical question to answer, but one thing i can tell u that Datastage Tx is not a</p><p>ETL tool &amp; this is not a new version of Datastage 7.5.</p></li><li><p>8/7/2019 What is the difference between a data warehouse and a data mart</p><p> 4/5</p><p>Tx is used for ODS source ,this much i know</p><p>Difference between Hashfile and Sequential File?</p><p>Hash file stores the data based on hash algorithm and on a key value. A sequential</p><p>file is just a file with no key column. Hash file used as a reference for look up.Sequential file cannot</p><p>Difference between Hashfile and sequential file is , searching a record is too fast in</p><p>hash file based on the hashkey, we can get the address of record directly in hashfilebased on the hashkey, and in sequential file it should search record sequential mode</p><p>only, it has to search for record by record, and we can remove duplicate records</p><p>based on the hash key in hashfile, we cannot in sequential file</p><p>What are Static Hash files and Dynamic Hash files?</p><p>The hashed files have the default size established by their modulus and separation</p><p>when you create them, and this can be static or dynamic.</p><p>Overflow space is only used when data grows over the reserved size for someone ofthe groups (sectors) within the file. There are many groups as the specified by the</p><p>modulus.</p><p>There are two types of hashfiles are there1.Static</p><p>2.dynamic</p><p>dynamic will use only when we dont know howmuch data will coming from thesource side, this will allow data loading grow automatically,</p><p>only we use static when we know the fixed amount of data we are trying to load inthe target DB,this is the scenario for use both types</p><p>2)Differences between star and snowflake schemas?The star schema is created when all the dimension tables directly link to the fact table. Sincethe graphical representation resembles a star it is called a star schema. It must be noted thatthe foreign keys in the fact table link to the primary key of the dimension table. This sampleprovides the star schema for a sales_ fact for the year 1998. The dimensions created are</p><p>Store, Customer, Product_class and time_by_day. The Product table links to the product_classtable through the primary key and indirectly to the fact table. The fact table contains foreignkeys that link to the dimension tables.</p><p>What is the difference between view and materialized view?View - store the SQL statement in the database and let you use it as a table. Everytime youaccess the view,? the SQL statement executes.materialized view - stores the results of the SQL in table form in the database. SQL statementonly executes once and after that everytime you run the query, the stored result set is used.Pros include quick query results.</p><p>Differences between star and snowflake schemas?</p></li><li><p>8/7/2019 What is the difference between a data warehouse and a data mart</p><p> 5/5</p><p>Star schema - all dimensions will be linked directly with a fat table.Snow schema - dimensions maybe interlinked or may have one-to-many relationship withother tables.</p></li></ul>