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Questions and Answers
What does dealing with changing dimension attributes refer to?
What does dealing with changing dimension attributes refer to?
Dealing with changing dimension attributes involves managing the changes in characteristics of dimension data in databases.
What 3 types are there to change the dimension? (Select all that apply)
What 3 types are there to change the dimension? (Select all that apply)
- Adding a new attribute/column (correct)
- Adding a new dimension record/row (correct)
- Overwrite the dimension attribute (correct)
- Deleting a dimension record
Explain the Type-1 dimension changing.
Explain the Type-1 dimension changing.
Overwriting the dimension attribute; it's easy to maintain and is often used for processing corrections.
What are the pros and cons of Type-1 dimension changing? (Select all that apply)
What are the pros and cons of Type-1 dimension changing? (Select all that apply)
Explain the Type-2 dimension changing.
Explain the Type-2 dimension changing.
What are the pros and cons of Type-2 dimension changing? (Select all that apply)
What are the pros and cons of Type-2 dimension changing? (Select all that apply)
Explain the Type-3 dimension changing.
Explain the Type-3 dimension changing.
What are the pros and cons of Type-3 dimension changing? (Select all that apply)
What are the pros and cons of Type-3 dimension changing? (Select all that apply)
What is the rapidly changing large dimension problem?
What is the rapidly changing large dimension problem?
How could we apply a Type-2 change in the context of rapidly changing dimension tables?
How could we apply a Type-2 change in the context of rapidly changing dimension tables?
What are mini-dimensions?
What are mini-dimensions?
Which entities might have rapidly changing large dimensions? (Select all that apply)
Which entities might have rapidly changing large dimensions? (Select all that apply)
The logical data model is usually structured as a _____. Why?
The logical data model is usually structured as a _____. Why?
What is a fact table?
What is a fact table?
A fact table holds...... A dimension table stores.....
A fact table holds...... A dimension table stores.....
The fact table consists of ____ types of columns. Name and describe them.
The fact table consists of ____ types of columns. Name and describe them.
What is an issue with performing relational queries using the star schema?
What is an issue with performing relational queries using the star schema?
Define Measures.
Define Measures.
What are the constructs of a STAR Schema?
What are the constructs of a STAR Schema?
Define Dimensions.
Define Dimensions.
Define facts.
Define facts.
Define Granularity.
Define Granularity.
What is an OLAP Cube?
What is an OLAP Cube?
What is an issue with the OLAP Cube?
What is an issue with the OLAP Cube?
A ____________ _____________ is a good relational DB for building a ______________ ____________________.
A ____________ _____________ is a good relational DB for building a ______________ ____________________.
OLAP cubes offer _____.
OLAP cubes offer _____.
What are key decisions made during the design of a dimensional model?
What are key decisions made during the design of a dimensional model?
What are Additive Measures?
What are Additive Measures?
What are Semi-Additive Measures?
What are Semi-Additive Measures?
What are Non-additive measures?
What are Non-additive measures?
What 2 types of fact nodes/tables are there?
What 2 types of fact nodes/tables are there?
What is a Transactional Fact Node?
What is a Transactional Fact Node?
What is a Snapshot Fact Node?
What is a Snapshot Fact Node?
Snapshots usually only have....
Snapshots usually only have....
A _____________ fact node represents events occurring at a point in time.
A _____________ fact node represents events occurring at a point in time.
Does a transactional or snapshot fact node have more dimensions?
Does a transactional or snapshot fact node have more dimensions?
Does a transactional or snapshot fact node have more measures?
Does a transactional or snapshot fact node have more measures?
What is a Surrogate Key? Why are they important?
What is a Surrogate Key? Why are they important?
Smaller surrogate keys translate into.....
Smaller surrogate keys translate into.....
Databases adopt an entity relationship diagram model, while data warehouses adopt a.....
Databases adopt an entity relationship diagram model, while data warehouses adopt a.....
What is a multidimensional data model?
What is a multidimensional data model?
Explain Online Analytical Processing (OLAP).
Explain Online Analytical Processing (OLAP).
Who has access to databases vs. data warehouses?
Who has access to databases vs. data warehouses?
Data warehouses provide..... Databases provide....
Data warehouses provide..... Databases provide....
Data warehouses manage _____________ data. Databases manage ______________ data.
Data warehouses manage _____________ data. Databases manage ______________ data.
Which contains different levels of granularity?
Which contains different levels of granularity?
While data warehouses support complex transactions, databases can only do....
While data warehouses support complex transactions, databases can only do....
Transactions for data warehouses are:
Transactions for data warehouses are:
What are Senior Business Management Sponsor(s)? Why are they important?
What are Senior Business Management Sponsor(s)? Why are they important?
What is Compelling Business Motivation?
What is Compelling Business Motivation?
Define feasibility.
Define feasibility.
What's a good economical justification for developing a data warehouse?
What's a good economical justification for developing a data warehouse?
When end-users are using the data warehouse, what is the main challenge? What's a potential solution?
When end-users are using the data warehouse, what is the main challenge? What's a potential solution?
What should be the first step when developing a data warehouse?
What should be the first step when developing a data warehouse?
What are the 4 Steps to the Dimensional Modeling Design Process?
What are the 4 Steps to the Dimensional Modeling Design Process?
Explain 1. Select business process.
Explain 1. Select business process.
Explain 2. Declare granularity.
Explain 2. Declare granularity.
Explain 3. Identify Dimensions.
Explain 3. Identify Dimensions.
Explain 4. Identify Facts.
Explain 4. Identify Facts.
What question should you ask to determine if an entry is a fact or not?
What question should you ask to determine if an entry is a fact or not?
What are dimensions?
What are dimensions?
What are the 2 main purposes of dimensions?
What are the 2 main purposes of dimensions?
Define understandability regarding dimension modeling.
Define understandability regarding dimension modeling.
What's the effect on query performance when adding dimensions?
What's the effect on query performance when adding dimensions?
How should a dimension modeling/design be extensible?
How should a dimension modeling/design be extensible?
What do we use if no property of the fact can fulfill the purpose of the primary key?
What do we use if no property of the fact can fulfill the purpose of the primary key?
Although surrogate keys seem like they're replacements for primary keys, all DWs should....
Although surrogate keys seem like they're replacements for primary keys, all DWs should....
What is Normalization? Why do it?
What is Normalization? Why do it?
What is snowflaking?
What is snowflaking?
What are disadvantages of normalization/snowflaking?
What are disadvantages of normalization/snowflaking?
What are the 3 Measure Types?
What are the 3 Measure Types?
Describe Additive Measures.
Describe Additive Measures.
Describe Semi-Additive Measures.
Describe Semi-Additive Measures.
Describe Non-Additive Measures.
Describe Non-Additive Measures.
What is a Periodic/Snapshot Fact Table?
What is a Periodic/Snapshot Fact Table?
Measures in the fact table represent an event that..... Measures in the fact node represent.....
Measures in the fact table represent an event that..... Measures in the fact node represent.....
Periodic fact tables allow one to measure the __________ of an organization.
Periodic fact tables allow one to measure the __________ of an organization.
In a PFT, here is _______ fact table row per ________ __________.
In a PFT, here is _______ fact table row per ________ __________.
In a TFT, there are more ________________, but less _______________ than a PFT. Why?
In a TFT, there are more ________________, but less _______________ than a PFT. Why?
What is a Factless Fact Table?
What is a Factless Fact Table?
What is an example of a Factless Fact Table being needed?
What is an example of a Factless Fact Table being needed?
How do you determine events that did not occur?
How do you determine events that did not occur?
SURROGATE KEYS SHOULD BE -__ INTEGERS.
SURROGATE KEYS SHOULD BE -__ INTEGERS.
How do surrogate keys increase performance?
How do surrogate keys increase performance?
Study Notes
Data Warehousing Concepts
- The logical data model structure commonly uses a Star Schema due to its user-friendly navigation and better performance in relational queries.
- A fact table serves as the central table in a data warehouse, containing quantitative information for analysis, often stored in a denormalized format.
- Fact tables hold the data to be analyzed while dimension tables provide context about how the data can be analyzed.
- Fact tables consist of two types of columns:
- Foreign key columns for joining with dimension tables.
- Measures columns containing data to be analyzed.
- Access time can be an issue when performing relational queries using star schema structures.
- Measures are core elements in the dimensional model, representing quantitative values, and can be summed, averaged, or manipulated mathematically.
Star Schema Constructs
- A Star Schema includes:
- Fact Node: Central table with measures.
- Dimension Node: Dependent tables that provide context.
- Dimension Edge: Relationships between dimension tables and facts.
- Dimensions are companion tables containing characteristics that describe facts.
- Facts are specific measurements about the entity being managed, e.g., financial metrics like totals or success rates.
Granularity and OLAP
- Granularity refers to the level of division of an entity into attributes, impacting data detail.
- An OLAP Cube is a three-dimensional array that allows for complex data analysis.
- Data sparsity is a common issue with OLAP cubes, often resulting in many empty cells.
Measure Types
- Three types of measures:
- Additive: Can be summed across all dimensions (e.g., total sales).
- Semi-Additive: Can be summed in some dimensions only (e.g., account balances).
- Non-additive: Cannot be summed at all (e.g., percentages).
Fact Tables
- Two types of fact nodes:
- Transactional Fact Nodes: Represent events at a specific time (e.g., retail sales).
- Snapshot Fact Nodes: Represent data snapshots at the end of a period (e.g., monthly account balances).
- A periodic/snapshot fact table summarizes measurement events over standard time periods, whereas transactional tables capture every single transaction event.
Data Warehouse vs. Database
- Databases focus on current data and support operational transactions, while data warehouses manage historical data and offer insights for decision-making.
- Data warehouses often contain multiple granularity levels compared to databases.
Project Planning and Design
- Senior Business Management Sponsors are essential for funding and utilizing the data warehouse.
- Compelling Business Motivation aligns the data warehouse with strategic goals.
- Feasibility emphasizes the importance of clean data for operational success.
- Developing a data warehouse involves understanding user requirements and focusing on dimensions and measures.
Dimensional Modeling
- The four-step design process for dimensional modeling:
- Select business processes.
- Declare the granularity of data attributes.
- Identify dimensions providing context.
- Identify facts representing quantitative data.
Change Management in Dimensions
- Types of dimension changes:
- Type-1: Overwrites existing dimensions (loses historical data).
- Type-2: Adds a new record for changes (keeps historical data but uses more space).
- Type-3: Adds new attributes/columns to keep current and previous values while minimizing new rows.
Surrogate Keys
- Surrogate keys are system-generated unique keys beneficial for identifying rows in fact tables where no single primary key is available. They enhance performance through efficient indexing and joining.
- Dealing with attributes in data dimensions often requires consideration of whether to overwrite, add, or change attributes to maintain data integrity and historical context.### Rapidly Changing Large Dimension Problem
- Involves extremely large dimensions where attributes undergo constant change.
- Affects maintenance and performance as dimensions grow, especially when using Type-2 changes to track historical data.
- Relevant examples include:
- Government agencies managing dimensions with over 100 million people.
- Large retail stores with several million product entries.
- Insurance companies maintaining millions of automobile records.
Type-2 Change Application
- Type-2 changes involve adding new records to capture historical data.
- Implemented through the use of mini-dimensions to manage attributes that frequently change.
Mini-Dimensions
- Mini-dimensions isolate rapidly changing attributes of a larger dimension.
- These mini-dimensions function as stand-alone entities and connect directly to fact tables without snowflaking, optimizing database structure.
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Test your knowledge of data warehousing concepts with these flashcards. Covering key elements such as star schema and fact tables, this quiz helps reinforce your understanding of data models and their structures. Ideal for students and professionals in data management.