If you are looking for Cognos Interview Questions And Answers For Experienced or Freshers, you are the right place. Here Mindmajix sharing a list of 60 real-time interview questions on Cognos, Cognos framework and Cognos report studio. These questions will help you to crack your next job interview and acquire a dream career as a Cognos developer.
|Tableau Desktop||IBM Cognos|
|Tableau Desktop provides a feature to import and visualize huge data sets, enables users to drill down into the data and also allows to make queries.||IBM Cognos makes it easy for users to dynamically explore data relations by transforming data into metadata.|
|Tableau Desktop makes it very easy to use and makes it very comfortable for users who are not explicitly data experts to explore the necessary data without any issues.||IBM Cognos is a wholesome platform for data experts alone as it is not that easy simple enough for users with average skills to explore and learn it.|
|Tableau Desktop works on both Windows and Macintosh OS environments and also has a web-based version||Microstrategy works only on Windows, Linux and Macintosh OS environments|
|Tableau Desktop is targeted to be used in Small, Medium to Larger enterprises||IBM Cognos is targeted to be used in Small, Medium and Larger enterprises as well.|
Cognos Interview Questions And Answers
Q1. What is Dynamic Cube?
Ans: Dynamic Cubes are in-memory OLAP cubes that load data directly from relational data sources that are structured in a star or snowflake schema
- Introduced as a new feature from IBM Cognos BI 10.2
- The Cognos Dynamic Cubes technology is part of the IBM Cognos BI query stack
- The goal of IBM Cognos Dynamic Cubes is to provide quick response to reports and analyses on large volumes of data.
- Enabling high-performance interactive analysis over terabytes of data
2. Cognos Dynamic Cube solution consists of what elements?
Ans: IBM Cognos Dynamic Cube consists of the following elements, they are:
- IBM Cognos Cube Designer
- IBM Cognos Dynamic Cubes Server
- Aggregate Advisor (part of IBM Cognos Dynamic Query Analyzer)
3. When to use Cognos Dynamic Cubes?
Ans: Data warehouse with star or snowflake schema
- A server with adequate memory
- A database with approximately 25 million or more fact table rows
4. Cognos Dynamic Cubes support which databases?
Ans: Cognos Dynamic Cubes support various databases.
Supported Databases (in the current 10.2 release) include IBM DB2, IBM Netezza, Microsoft SQL Server, Oracle, Teradata.
Q5. What is the difference between Cognos Dynamic cube and Transformer/TM1 cube?
TM1 Cube - In-memory cube technology with writeback support
PowerPlay Cube - File-based cube technology
Dynamic Cube - Provides extensive in-memory caching for performance
TM1 Cube - Is optimal for write-back, what-if analysis, planning and budgeting, or other specialized applications
PowerPlay Cube - Interactive analysis experience to a large number of users
Dynamic Cube - Is optimal for read-only reporting and analytics
TM1 Cube - Star or snowflake data structure is not required
PowerPlay Cube - Data source is an operational or transactional system. Do not require star or snowflake data structure
Dynamic Cube - Star or snowflake schema is required
TM1 Cube - Aggregation occurs on demand
PowerPlay Cube - File-based cube with preaggregation
Dynamic Cube - Supports in-memory aggregation
6. Where Dynamic Cube resides in Cognos BI Environment?
Ans: Dynamic cube are in-memory OLAP containers that reside within the DQM server
7. Can you explain Dynamic Cube Lifecycle in Cognos?
- Model and Publish (Warehouse and CM)
- Deploy and Manage (Dynamic Cube Server, CM)
- Reporting and Analytics (Dynamic cube, Logs)
- Optimize (Warehouse, CM, Logs)
8. What is Cognos Cube Designer?
- Cognos Cube Designer is used to model Dynamic Cubes
- Install IBM Cognos Cube Designer in the same location as IBM Cognos Framework Manager
- We need a JDBC data source connection created in Cognos Administration
9. Explain about Cognos Cube Designer modelling workflow?
Ans: First model your cube definition in Cognos Cube Designer
- select the database schema
- import the required metadata
- define the dimensions and measures
- Creating Dynamic cube
- Auto-generate cube
- Use primary-foreign key relationship to populate dimensions
- Manually model the cube
- Deploy your dynamic cube to BI server
- Quick-deploy options in Cognos Cube Designer with Publish Option
- An option that is deselected here must be accomplished manually in FM or in Cognos Connection.
10. How do you administrate Dynamic Cube?
Ans: Administration tasks include assigning the cube to the QueryService instance, starting it, monitoring its health, and refreshing its contents.
- Start/Stop the Cube
- Monitoring Cube
- Managing the cache
- Scheduling a refresh of the cache
Cognos Interview Questions For Developers
11. Explain about Aggregate Advisor?
Ans: Aggregate Advisor is a performance optimization utility
- Part of the Dynamic Query Analyzer
- Suggest database aggregate tables, in-memory aggregate, or both.
- Makes use of a cube’s model and statistics
- Make use of workload log files that are generated from the execution of reports
- The expectation is that the dynamic cube is published in the Content Store, can be started successfully, and that reports and analysis run and return correct results.
- After a cube is restarted, the aggregates execute the necessary SQL statements to retrieve the summarized values and place the values in its aggregate cache for subsequent use during query processing.
- Run during off-peak, non-critical business hours
12. Explain about Aggregate Cache?
Ans: Cognos Dynamic Cube supports two types of pre-computed aggregate values:
- Stored in in-database tables (in-database aggregate)
- Stored in an in-memory aggregate cache
- Aggregate Advisor can suggest a collection of in-memory aggregate
- In-memory aggregate does not require the involvement of DBA
- Recommendations are stored in Content Manager and take effect next time a cube is started.
- The size of the aggregate cache is specified in the properties of a dynamic cube - Maximum amount of memory to use for the aggregate cache (MB).
13. What is Aggregate cache size?
Ans: Only enough memory that is required to hold the defined aggregates is used.
Example: 90 MB can hold the aggregates for gosldw_sales, and the aggregate cache size is set to 1 GB, only 90 MB of memory is used. Over time, if the underlying fact tables grow, the aggregates are allowed to grow to the specified maximum of 1 GB.
Should not use more than 30 GB for the aggregate cache.
14. What is Model Durability?
Ans: All of the following criteria must be met in order to have what is considered to be a durable model:
- There is a design language created for the model that is not the same as the locales the users can choose from. For English, the design language is typically English(Zimbabwe).
- The design language name of all namespaces, query subjects, and query items that are published in a package must never change after the package is initially published. Other language names can change as needed, though.
- The structure of a published package's namespace(s), query subjects, query items, dimensions, shortcuts, etc, must not change over time. This structure is stored in a specification's definition, along with the design language's names, so this is the reason these must not change.
- In IBM Cognos 8.4.1 the element must exist in model.xml. In IBM Cognos 10 the project level property Use Design Locale for Reference ID must be set to true.
15. It the model is not durable, then what would you change to make model durable?
Ans: It the model is not durable, then the following changes must be done to make the model durable:
- If the model does not already have a design language, then:
- Add the necessary design language to the model and add it to the languages of each package based on the model. Save and close the model.
- Using an XML or text editor, open the model.xml file and near the top of the file, change the value of en to en-zw.
- For IBM Cognos 8.4.1, insert a blank line into the model.xml file under the just modified element and add true to the new blank line.
- For IBM Cognos 10, set the project level property Use Design Locale for Reference ID to a value of true
16. What is New Content Durability?
Ans: All new content developed with IBM Cognos BI will be durable, as long as the model is durable. Existing non-durable content can be made durable by appropriately replacing the non-durable components of those specifications with durable components. Existing content is generally made durable over time as the content gets updated for reasons other than durability
17. How do you create security features to cubes?
Ans: For creating security features in cubes we can use the user class views and dimension views.
Dimension views help in hiding certain data from the cube depending on what view you are using.
Then we can use the user class views to the cubes for making that data available for a certain role or group.
We can also use password protection is another way of providing security to the cubes.
18. What is the size of your cube?
Ans: It may have 300mb; 400mb depends on the position, Optimum size for a cube is up to 2GB;
19. What is the user class in Cognos?
Ans: A user class is a group of users who need access to the same data and have the same access privileges. The administrator creates the catalog and user classes. Other people in an organization may also create and maintain user classes for the employees in their own department or area.
You can add user classes to a catalog if you created the catalog or you are working with a personal copy of a distributed catalog and your administrator gave you the privilege to add and modify user classes.
Cognos Framework Manager Interview Questions
20. What is the Framework Manager?
Ans: Framework Manager is a tool that allows you to make data sources known for use within the various Cognos suites and allows you to add additional logic and details. Within a logical Cognos architecture, a Framework Manager model contains the logic and information required for one of the Cognos tools to use a data source.
21. Explain IBM Cognos Framework Manager Model?
Ans: IBM Cognos Framework Manager is a metadata modelling tool that drives query generation for IBM Cognos software. A model is a collection of metadata that includes physical information and business information for one or more data sources. IBM Cognos software enables performance management on normalized and denormalized relational data sources and a variety of OLAP data sources.
22. What are the layers available in the Framework Manager Model?
Ans: The Framework Manager model consists of three layers:
- Database layer
- Logical Layer
- Dimensional layer
23. What is the IBM Cognos Framework Manager model database layer?
Ans: The physical, or database, the layer contains a database query subject for every table in the physical data model. The database layer also contains alias shortcuts, which behave as if they were a copy of the original object with completely independent behaviour.
24. What is the IBM Cognos Framework Manager model logical layer?
Ans: The logical layer contains query subjects that draw data from the database query subjects and present it in a more consumable format.
25. What is the IBM Cognos Framework Manager model dimensional layer?
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Ans: The dimensional layer contains the hierarchies and measure dimensions for publication to a package. Each dimension in the logical layer has a dimension in the dimensional layer with one or more hierarchies defined. The hierarchies usually include the caption field twice, once as a caption for the level, once as an attribute that can be used in report filters. All hierarchies are sorted.
26. What is the IBM Cognos Framework Manager model security?
Ans: No security is defined for the IBM Cognos Framework Manager model other than the provision for filtering by the tenant_id parameter on the physical layer. These query subject filters can be converted to security filters that are based on user IDs, allowing multi-tenant access to one database.
27. What is Query mode?
Ans: The IBM Predictive Maintenance and Quality reports use IBM Cognos Compatible Query Mode, which is the supported mode for all of the reports.
28. What is IBM Predictive Maintenance and Quality?
Ans: With IBM Predictive Maintenance and Quality, you can monitor, analyze, and report on information that is gathered from devices. In addition, recommendations for actions can be generated by Predictive Maintenance and Quality.
- IBM Predictive Maintenance and Quality is an integrated solution that you can use to perform the following tasks:
- Predict the failure of an instrumented asset so that you can prevent costly unexpected downtime.
- Make adjustments to predictive maintenance schedules and tasks to reduce repair costs and minimize downtime.
- Quickly mine maintenance logs to determine the most effective repair procedures and maintenance cycles.
- Identify the root cause of asset failure faster so that you can take corrective actions.
- Identify quality and reliability issues definitively and in a timely way.
29. What is Orchestration in IBM Predictive Maintenance and Quality?
Ans: The orchestration is the process that ties activities in IBM Predictive Maintenance and Quality together.
Message flows: Orchestration is achieved with message flows in IBM Integration Bus.
Example of an orchestration XML file: An example file, inspection.xml, demonstrates the purpose and structure of an orchestration file.
Generic batch orchestration: Generic batch orchestration provides capabilities to run a scheduler flow and invoke any IBM SPSS batch job by taking inputs from a configurable XML file instead of developing separate message flows for a specific use case.
30. Can you explain about Message Flows?
Ans: The orchestration is achieved with message flows in IBM Integration Bus.
The following activities can be tied together:
- Acquiring and storing data
- Aggregating data
- Running predictive models
- Feeding data back to external systems or starting external processes
Message flows are supplied with IBM Predictive Maintenance and Quality and must be customized with IBM Integration Bus. The message flows are organized into the following applications:
Cognos Interview Questions For Experienced
31. How Framework Manager Uses Cardinality
Ans: Cardinality is used by the query engine to:
Identify query subjects that behave as facts and dimensions
1..n cardinality implies fact data on the n side and dimension data on the 1 side
Avoid double counting fact data
Support loop joins in star schema models
Cardinality is applied in the context of a query
Query subjects may be facts or dimensions depending on the other query subjects included in the query
32. What are Determinants?
Ans: Determinants Feature first introduced in Cognos 8 used to provide control over granularity when aggregating
- Reflects granularity by identifying groups or subsets of data in a query subject
- Used to ensure that repeating data is aggregated correctly
- Are set during import based on unique key and index information in a database
- Used by Framework Manager to determine levels in default hierarchy when auto-generating regular dimensions from query subjects
33. When and how should you use Determinants?
Ans: When do I need to use determinants:
- When dimensions connect to fact tables at levels of granularity that have repeating keys
- When there is a need to count or perform aggregate functions on a key or attribute that is repeated
- To avoid generating a ‘distinct’ clause on distinct keys
34. What is Modle Advisor?
Ans: Use Model Advisor – Check early and often
Model Advisor is a useful tool for detecting common modelling issues, Cardinality issues, Potential join path conflicts, Incorrect determinants. Easy to configure to check as for as much or as little as desired, Run after import to check for areas that need further investigation, Run again periodically to identify potential issues as you work, Direct links to the problem area and Help.
35. What is Dimensional Modeling for Report and Analysis?
Ans: Dimensionally modelled relational (DMR) constructs in Classic Query Mode
- Logical dimensional layer over top of a relational model
- Single measure dimension and one or multiple regular dimensions
- Enables drill-up/drill-down analysis in the studios
- Dimensional layer can be applied over any star schema model
- Not a requirement that the underlying data source be a star schema design
- Dimensions and measure dimensions are constructed from model query subjects or database query subjects
- At runtime, queries are run to spin a virtual cube on disk to simulate the OLAP style analysis capabilities
36. What are Regular Dimensions?
Ans: Regular dimensions created from model query subjects or database query subjects
- Define hierarchies to organize levels and define drill paths
- You can specify multiple hierarchies in a single dimension
- Define levels, business keys and caption
- Create from scratch using Dimension Definition dialog
- Use “Merge in New Regular Dimension” or “Convert to Regular Dimension” capabilities
- The dimension will be auto-generated based on query subject definition
- Default hierarchy created
- Levels derived from determinants set
- May need to be adjusted based on requirements
37. What is Measure Dimension?
Ans: Create measure dimension
- Collection of facts
- Create measure dimension using Dimension Definition dialog or “Convert to Measure Dimension” capability
- Add existing measures or create calculations
- Define scope relationships
- Dictates level at which measures are available for reporting
- Scope relationship will be detected by the Framework Manager using the underlying join paths between query subjects and fact query subject
- Scope relationships can be defined and reviewed in the Dimension Map
38. What is Query Generation?
Ans: By default, Framework Manager will use Cognos SQL to create Query Subjects
In Classic Query Mode, at runtime, native SQL optimized for the data source is generated and passed down through to the data source
- RQP (Relational Query Planner) plans the query and then passes it off to UDA (Universal Data Access)
- UDA component has a series of gateway files that control SQL generation for specific RDBMS (DB2, Oracle, MS SQL Server, etc)
- UDA generates the native SQL and executes it against the RDBMS
Copy of the query engine local in the Framework Manager install
- Used for importing metadata, testing query subject, generating SQL and validation of expressions
In Dynamic Query Mode, requests are sent to the Query Service for processing
- No query service running locally on the FM side
Framework Manager will include passing the necessary elements in the model to Query Service on the server
- Result set and generated SQL for the query will be part of the response back to FM.
- This is the case testing objects and evaluating expressions
39) What is the SQL Generation?
Ans: Use minimized SQL when possible
Certain conditions will trigger as view SQL and override this setting:
- Determinants on a model query subject
- Relationships between model query subjects
- Filters, macros or calculations in data source query subjects
“As view” SQL not always bad
- Sometimes required to force certain behaviours
- Can be necessary to ensure predictable query results
- Know your requirements and your data
40. What is Dynamic Query Mode (DQM)?
Ans: A new Dynamic Query Processing Mode (DQM) to the existing query service designed to improve query performance.
- Enhanced Java-based query execution mode introduced in 10.1 to support select OLAP sources
- Leverages JDBC access to supported data sources
- Support has been extended in 10.1.1 to include the following relational sources
- DB2, Netezza, Teradata, Oracle, MS SQL Server
- Can be used with 64-bit report server included in 10.1.1 to enable administrators to better leverage memory
- Has robust caching capabilities to help improve query performance
- In-memory caching of the query plan and query results
- Security aware
- SQL generation optimization for relational sources
- A new implementation to support dimensional modelling of relational data sources
- OLAP over Relational
- Not the same implementation as DMR incompatible mode
- Simpler, more efficient queries than DMR
- Null suppression optimizations
- Master-detail optimizations available in reports
- Treats OLAP over Relational as a true OLAP source
- Enables report authors to fully leverage member functions and OLAP style reporting techniques
- Dramatic performance benefits available by leveraging caching capabilities
41. Explain about working with Dynamic Query Mode?
Framework Manager 1.x, 8.x and 10.x includes a full copy of the data access stack
- Used for import, testing and evaluating query subjects, relationships, etc.
- Framework Manager machine requires DB client software installed
With the introduction of 10.1.1, Framework Manager enables users to work in Dynamic Query mode or Compatible mode
- Can enable DQM at the project level or package level
Working in dynamic mode will leverage the always leverage the query service on the server
- Import, testing, and evaluation of objects
The compatible mode will continue to leverage the local query components
- CQE, UDA, etc.
New metadata import mechanism available for DQM
- JDBC import that leverages RELMD service
- Nothing local required on FM environment
- Dramatic improvement in performance for very large imports
A new mechanism to test objects and evaluate expressions
- Client-server type model
- Framework Manager will send a request to query service
- Generated query and result set will be returned
On-demand evaluation of expressions in the editor
- Option to turn off “per-click” evaluation in the expression editor
Can work in compatible mode and enable dynamic query mode for packages
- Can enable dynamic mode on a package by package basis
- The mechanism in place to ensure data sources are enabled
Can switch an existing model to the dynamic mode
- All objects in the model will be evaluated by query service
- For existing models, more efficient to enable dynamic mode on a package basis to evaluate
42. Working in Dynamic Mode – OLAP over Relational?
Ans: Some differences between DMR and OLAP over Relational
- OLAP over Relational much closer to true OLAP experience
- DQM provides 2 mechanisms for member ordering
- Ascending order by member caption
- Not consistent in compatible mode (varies by query/data source)
- Option available in Framework Manager to explicitly set
- Set for metadata tree in studios
- Set for data values returned
Null suppression capabilities
- True OLAP style null suppression available
- Controls available at a studio level
Null handling in the calculation
- Configuration available on the server to have 0 substituted for nulls for mathematical calculations
43. What is the package in Cognos?
Ans: IBM Cognos Package or Report. You can import query items, and the associated filters and prompts, from IBM Cognos packages and reports. You do this by choosing the Package or Report data source type and browsing and selecting from the available metadata.
44. What is Impromptu in Cognos?
Ans: Cognos Impromptu is an intuitive, user-friendly system that enables non-technical personnel to quickly and easily design and distribute business intelligence reports.
45. What is the use of Cognos tm1?
Ans: IBM Cognos TM1 (formerly Applix TM1, formerly Sniper TM/1) is enterprise planning software used to implement collaborative planning, budgeting and forecasting solutions, as well as analytical and reporting applications.
46. What is a Cognos Controller?
Ans: IBM Cognos Controller is part of an integrated Financial Close Management (FCM) solution, built on an efficient, purpose-built platform. It helps you deliver complete financial results, create financial and management reports, and provide the CFO with an enterprise view of key ratios and metrics.
47. What is Cognos Planning?
Ans: Flexible enterprise software for planning, budgeting, forecasting and analysis. IBM Cognos Planning enables you to develop plans, budgets and forecasts faster and more efficiently. Cognos Planning lets you create, compare and evaluate business scenarios.
48. What is tm1 Architect?
Ans: IBM Cognos TM1 is a solution with a client-server architecture and TM1 Architect is one of the standard TM1 client components that can connect to the TM1 server. The key components of TM1 are TM1 Architect, TM1 Perspectives, TM1 Web and Turbo Integrator.
49. What is tm1 perspective?
Ans: TM1 Perspectives is a standard TM1 standalone application and needs Microsoft Excel to run. It uses Cube Viewer features while taking advantage of MS Excel functionality via an add-in for Excel.
50. What is tm1 Web?
Ans: IBM Cognos TM1 Web uses a multi-tiered architecture that enables users to access and interact with Cognos TM1 data using any supported web browser. The IBM Cognos TM1 Web multi-tiered architecture includes web client, web application server and data component tiers.
Cognos Report Studio Interview Questions For Experienced
51. What is the extension of the framework manager project file?
Ans: The extension for framework manager project file is a store in the file system with extension .cpf ( Cognos Project File )
52. What is the difference between the model and package in Cognos?
A model serves as an insulating layer between IBM Cognos BI reporting users and the database. Packages are model subsets that ensure users are provided with data appropriate for the reporting they need to do, and that the data is structured in ways that make sense from a business perspective.
Creating models and publishing packages are tasks that should be planned carefully. Models and packages that are well-designed from the start ensure that user requirements are met, data is secure, and your IBM Cognos BI application can be easily administered.
To understand the modelling and packaging process, users can study the sample models, packages, and reports provided with IBM Cognos BI. For information about setting up the samples, see the IBM Cognos Administration and Security Guide.
For IBM Cognos BI reporting, models and packages are created using Framework Manager. The following topics provide an overview. For more information, see the IBM Cognos Framework Manager User Guide.
53. What is the different type of securities can we apply in framework manager?
Ans: In IBM Cognos Framework Manager, security is a way of restricting access to metadata and data across IBM Cognos products.
There are different types of security in Framework Manager:
- Data Security: You create a security filter and apply it to a specific query subject. The filter controls the data that is shown to your users when they set up their reports.
- Object Security: You secure an object directly by allowing users access to the object, denying users access to the object, or keeping it hidden from all users.
- Package Security: You apply security to a package and identify who has access to that package.
54. What is looping and how to avoid it in framework manager?
Ans: Loop joins in the model are typically a source of unpredictable behaviour. This does not include star schema loop joins.
When cardinality clearly identifies facts and dimensions, IBM Cognos software can automatically resolve loop joins that are caused by star schema data when you have multiple fact tables joined to a common set of dimension tables.
In the case of loop joins, ambiguously defined query subjects are the primary sign of problems. When query subjects are ambiguously defined and are part of a loop join, the joins used in a given query are decided based on a number of factors, such as the location of relationships, the number of segments in join paths, and, if all else is equal, the alphabetically first join path. This creates confusion for your users and we recommend that you model to clearly identify the join paths.
55. What is the difference between star schema and snowflake schema in Cognos?
Ans: Star and snowflake schema designs are mechanisms to separate facts and dimensions into separate tables. Snowflake schemas further separate the different levels of a hierarchy into separate tables.
Star schemas - A star schema is a type of relational database schema that is composed of a single, central fact table surrounded by dimension tables.
Snowflake schemas - The snowflake schema, sometimes called snowflake join schema consists of one Fact table connected to many dimension tables, which can be connected to other dimension tables.
56. What is warehouse cubing?
Ans: IBM DB2 Warehouse Cubing Services is designed to provide a multidimensional view of data stored in a relational database. With Cubing Services, you can create, edit, import, export, and deploy cube models over the relational warehouse schema. Cubing Services also provides optimization techniques to dramatically improve the performance of OLAP queries, a core component of data warehousing and analytics.
57. What are the Fact Tables?
Ans: A fact table is a table in a star or snowflake schema that stores facts that measure the business, such as sales, cost of goods, or profit. Fact tables also contain foreign keys to the dimension tables. These foreign keys relate each row of data in the fact table to its corresponding dimensions and levels.
Cubing Services also supports fact tables that are logical, meaning that the fact table of a facts object in a cube model can be a view.
58. What are the Dimension tables?
Ans: A dimension table is a table in a star or snowflake schema that stores attributes that describe aspects of a dimension. For example, a time table stores the various aspects of time such as year, quarter, month, and day. A foreign key of a fact table references the primary key in a dimension table in a many-to-one relationship.
59) What are the cube models?
Ans: The DB2 Warehouse cube model represents a logical star schema or snowflake schema and groups relevant dimension objects around a central facts object.
Each dimension can have multiple hierarchies. The structural information about how to join the tables that are used by the facts object and dimensions is referenced by the cube model. Also stored in the cube model is enough information to construct SQL queries and to retrieve OLAP data. Other reporting and OLAP tools that understand the cube model and that can display multiple views of a specific dimension can benefit from using the cube model.
60) What is dimensional schema?
Ans: A database is comprised of one or more tables, and the relationships among all the tables in the database are collectively called the database schema. Although there are many different schema designs, databases used for querying historical data are usually set up with dimensional schema design, typically a star schema or a snowflake schema.
There are many historical and practical reasons for dimensional schemas, but the reason for their growth in popularity for decision support relational databases is driven by two main benefits:
- The ability to form queries that answer business questions. Typically, a query calculates some measure of performance over several business dimensions.
- The necessity to form these queries in the SQL language, used by most RDBMS vendors.