Understanding Data Warehouse Schema Types Quiz
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Questions and Answers

What does a star schema in a Data Warehouse consist of?

  • One dimension table and multiple fact tables
  • One fact table and multiple dimension tables (correct)
  • Multiple fact tables only
  • Multiple dimension tables only

    • Which type of schema is optimized for querying large data sets?

  • Galaxy schema
  • Star schema (correct)
  • Snowflake schema
  • 5 Schema

    • What is contained in a Fact Table in a Data Warehouse system?

  • All the facts or business information (correct)
  • Name and description of records
  • Only dimension tables
  • Aggregates associated with the data

    • Why is the star schema called as such?

    <p>Because its structure resembles a star</p> Signup and view all the answers

    Which type of schema includes a center that can have one fact table and multiple dimension tables?

    <p>Star schema</p> Signup and view all the answers

    What does a Data Warehouse schema define?

    <p>The entire database structure</p> Signup and view all the answers

    What is the purpose of a fact table in a Data Warehouse system?

    <p>To store direct facts and connect with dimension tables</p> Signup and view all the answers

    How are dimension tables organized in a Star Schema?

    <p>With descriptive attributes and uniquely identified by a primary key</p> Signup and view all the answers

    What is a characteristic of a Star Schema design?

    <p>Dimension tables are normalized</p> Signup and view all the answers

    How are dimension tables connected to fact tables in a Star Schema?

    <p>Using foreign keys</p> Signup and view all the answers

    Which step comes first in designing a Star Schema?

    <p>Identify the business process</p> Signup and view all the answers

    What is stored in a fact table in a Data Warehouse system?

    <p>Key and measure data</p> Signup and view all the answers

    What is the main difference between a snowflake schema and a star schema?

    <p>Dimension tables in a snowflake schema are normalized, while in a star schema they are not.</p> Signup and view all the answers

    How is the structure of dimension tables different in a snowflake schema compared to a star schema?

    <p>Dimension tables in a snowflake schema are connected to normalized additional tables.</p> Signup and view all the answers

    What does the lowest level of aggregation or summary analysis refer to in the context of a fact table?

    <p>The highest level of detail within the fact table</p> Signup and view all the answers

    Why are dimension tables normalized in a snowflake schema?

    <p>To reduce redundancy and improve data integrity</p> Signup and view all the answers

    What is the purpose of having multiple levels and hierarchies in the dimension tables of a snowflake schema?

    <p>To provide different levels of detail for analysis</p> Signup and view all the answers

    What is one of the cases proposed by Ralph Kimball where a snowflake implementation is not only acceptable but also key to successful design?

    <p>Large customer dimensions with little detail for anonymous visitors</p> Signup and view all the answers

    What type of product dimensions are mentioned as suitable for a snowflake schema?

    <p>Financial product dimensions with unique attributes per product</p> Signup and view all the answers

    What is a characteristic of the snowflake schema mentioned in the text?

    <p>Requires more maintenance efforts due to numerous lookup tables</p> Signup and view all the answers

    In a galaxy schema, what relationship exists between fact tables and dimension tables?

    <p>Multiple fact tables share dimension tables</p> Signup and view all the answers

    What analogy is used to describe a galaxy schema?

    <p>Collection of stars</p> Signup and view all the answers

    Which type of schema involves attaching any one level from a hierarchy to the Fact Table?

    <p>Star Schema</p> Signup and view all the answers

    What is another name for Galaxy Schema?

    <p>Fact Constellation Schema</p> Signup and view all the answers

    How are the dimensions organized in a Galaxy Schema?

    <p>Separated into separate dimensions based on hierarchy levels</p> Signup and view all the answers

    What is the main advantage of a Galaxy Schema?

    <p>Helpful for aggregating fact tables for better understanding</p> Signup and view all the answers

    How is a Galaxy Schema constructed?

    <p>By splitting a one-star schema into more Star schemas</p> Signup and view all the answers

    What is the primary characteristic of dimensions in a Galaxy Schema?

    <p>Large dimensions built based on hierarchy levels</p> Signup and view all the answers

    Which type of schema can be used to build a Galaxy Schema?

    <p>Star Schema</p> Signup and view all the answers

    Study Notes

    Data Warehouse Schema

    • A Data Warehouse system can have one or more fact tables, depending on the model type used to design the Data Warehouse.

    Fact Table

    • A fact table in a Data Warehouse system contains all the facts or business information that can be subjected to analysis and reporting activities.
    • A fact table holds fields that represent direct facts and foreign fields that connect the fact table with other dimension tables.

    Dimension Table

    • A dimension is a collection of reference information about a measurable in the fact table.
    • The primary key column of the dimension table uniquely identifies each dimension record or row.
    • Dimension tables are organized with descriptive attributes.
    • Examples of dimension attributes include: first and last name, birth date, gender, qualification, address, etc.

    Star Schema

    • A star schema is a simplest type of Data Warehouse schema, also known as Star Join Schema.
    • The star schema is optimized for querying large data sets.
    • The center of the star can have one fact table and a number of associated dimension tables.
    • The star schema is easy to understand and provides optimal disk usage.
    • The dimension tables are not normalized in a star schema.
    • The schema is widely supported by BI Tools.

    Characteristics of Star Schema

    • Every dimension in a star schema is represented with only one dimension table.
    • The dimension table should contain a set of attributes.
    • The dimension table is joined to the fact table using a foreign key.
    • The dimension tables are not joined to each other.
    • The fact table would contain key and measure.

    Steps in Designing Star Schema

    • Identify the business process.
    • Identify the measures or fact data.
    • Identify the dimension tables related to the fact table.
    • Find the lowest level of aggregation or summary analysis in the fact table.

    Snowflake Schema

    • A snowflake schema is an extension of the star schema where the dimension tables are connected to one or more dimensions.
    • The dimension tables are normalized, which splits data into additional tables.
    • The snowflake schema keeps the same fact table structure as the star schema.
    • In the dimension, it has multiple levels with multiple hierarchies.
    • From each hierarchy of levels, any one level can be attached to the fact table.

    When to Use Snowflake Schema

    • Large customer dimensions where, for example, 80 percent of the fact table measurements involve anonymous visitors.
    • Financial product dimensions for banks, brokerage houses, and insurance companies.
    • Multi-enterprise calendar dimensions because each organization has idiosyncratic fiscal periods, seasons, and holidays.

    Characteristics of Snowflake Schema

    • The main benefit of the snowflake schema is it uses smaller disk space.
    • It is easier to implement a dimension added to the schema.
    • Due to multiple tables, query performance is reduced.
    • The primary challenge is to perform more maintenance efforts because of the more lookup tables.

    Galaxy Schema

    • Multiple fact tables share dimension tables in the galaxy schema.
    • The galaxy schema is viewed as a collection of stars, hence called galaxy schema.
    • It is also called Fact Constellation Schema.

    Characteristics of Galaxy Schema

    • The dimensions in this schema are separated into separate dimensions based on the various levels of hierarchy.
    • For example, if geography has four levels of hierarchy like region, country, state, and city, then the galaxy schema should have four dimensions.
    • It is possible to build this type of schema by splitting the one-star schema into more star schema.
    • The dimensions are large in this schema which is needed to build based on the levels of hierarchy.
    • This schema is helpful for aggregating fact tables for better understanding.

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    Description

    Test your knowledge on star schema, snowflake schema, and galaxy schema in data warehousing. Learn about the differences in design and structure between these types of schemas.

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