Tài liệu Module 12: Working with Virtual Cubes docx

BETA MATERIALS FOR MICROSOFT CERTIFIED TRAINER PREPARATION PURPOSES ONLY Instructor Notes A virtual cube is an online analytical processing OLAP cube that combines or extracts data from

Contents

Overview 1

Lab B: Adding Calculated Members to a

Review 19

Module 12: Working with Virtual Cubes

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Instructor Notes

A virtual cube is an online analytical processing (OLAP) cube that combines or extracts data from one or more source cubes These cubes are called virtual because they consume no disk storage, other than metadata In this module, students learn when to use virtual cubes and the mechanics of how to build them in Microsoft® SQL Server™ 2000 Analysis Services

After completing this module, students will be able to:

! Understand when to use virtual cubes and know their benefits

! Know the rules for constructing meaningful virtual cubes

! Build virtual cubes by using the Virtual Cube Wizard

! Define calculated members in virtual cubes by using the Calculated Member Builder

Materials and Preparation

This section lists the required materials and preparation tasks that you need to teach this module

Required Materials

To teach this module, you need Microsoft PowerPoint® file 2074A_12.ppt

Preparation Tasks

To prepare for this module, you should:

! Read all of the student materials for this module

! Read the instructor notes and margin notes

! Complete the labs

! Review the Trainer Preparation presentation for this module on the Trainer Materials compact disc

! Review any relevant white papers that are located on the Trainer Materials compact disc

Presentation:

25 Minutes

Labs:

20 Minutes

iv Module 12: Working with Virtual Cubes

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Other Activities

Difficult Questions

Below are difficult questions that students may ask you during the delivery of this module and answers to the questions There materials delve into subjects that are within the scope of the module but are not specifically addressed in the content of the student notes

1 How does the enabling or disabling of levels in the source cube affect the enabling or disabling of levels in the virtual cube?

Enabling or disabling levels in the source cube does not affect the enabling or disabling of levels in the virtual cube Levels in the source cube are completely separate from levels in the virtual cube, so that, when users are using a virtual cube, they can access members for querying or for creating calculations down to the lowest level in the dimension, regardless of level enabling or disabling in the source cube

2 Can you add a virtual dimension to a virtual cube without also adding the dimension on which the virtual dimension depends?

No When you add a virtual dimension to a virtual cube, the regular dimension is added to the virtual cube automatically

3 Can you base virtual cubes on linked cubes?

Yes

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Module Strategy

Use the following strategy to present this module:

! Understanding Virtual Cubes Begin with a definition of virtual cubes and describe their characteristics Discuss virtual cube limitations and storage

! Obtaining Logical Results Explain that, when building a virtual cube from more than one source cube, students must follow some simple rules to obtain logical results Explain that they need to use dimensions and measures that the source cubes have in common—otherwise there is no analytical value in combining the cubes

! Building a Virtual Cube Introduce students to the Virtual Cube Wizard While giving the lecture, open the Virtual Cube Wizard on your computer and show students the various interfaces Describe the steps involved in creating a virtual cube—choosing the source cube, choosing the measures, choosing the dimensions, and finalizing the cube

! Creating Calculated Members Explain that calculated members can be added to virtual cubes by using the Virtual Cube Editor Describe the different ways to add calculated members

to virtual cubes—creating calculated members and importing them

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Overview

! Understanding Virtual Cubes

! Obtaining Logical Results

! Building a Virtual Cube

! Creating Calculated Members

A virtual cube is an online analytical processing (OLAP) cube that combines or extracts data from one or more source cubes These cubes are called virtual because they consume no disk storage other than metadata In this module, you will learn when to use virtual cubes and the mechanics of how to build them in Microsoft® SQL Server™ 2000 Analysis Services

After completing this module, you will be able to:

! Understand when to use virtual cubes and know their benefits

! Know the rules for constructing meaningful virtual cubes

! Build virtual cubes by using the Virtual Cube Wizard

! Define calculated members in virtual cubes by using the Calculated Member Builder

In this module, you will learn

about virtual cubes and how

to create them

2 Module 12: Working with Virtual Cubes

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Understanding Virtual Cubes

! Virtual Cube Characteristics

# Combine data from multiple cubes

# Provide users with a subset of a single cube

# Are used to limit user access to cube data

! Dimension Limitations

# Cannot slice dimensions

# Cannot include only some of a dimension’s levels

! Storage and Performance

# Can include MOLAP, ROLAP, and HOLAP cubes

# Provide endless cube flexibility

A virtual cube is a cube that combines or extracts data from one or more source

cubes In many respects, a virtual cube is to Analysis Server what a view is to a relational database management system (RDBMS)—it provides a different view

of the underlying data without storing any additional data except the metadata that defines the virtual cube

This module defines virtual cubes as being derived from source cubes

Source cubes are the cubes from which a virtual cube is derived

Virtual Cube Characteristics

To users and applications, a virtual cube is simply a cube It looks and behaves exactly like a source cube A virtual cube can be used to:

! Combine data from two or more source cubes For example, a cube containing sales data might be combined with a cube containing forecasts to measure actual sales versus forecast sales

If a virtual cube is based on more than one source cube, when the virtual cube is queried, it queries the source cubes in parallel

A virtual cube can combine up to 64 source cubes

! Provide users with a subset of the dimensions and measures from a single source cube This is useful when a source cube contains a great many measures and dimensions, and a group of users is interested in only a subset

! Provide users with a subset of the dimensions and measures from a single source cube as a security measure For instance, the source cube might contain a profit measure that certain users or groups of users are not allowed

A virtual cube combines or

extracts data from one or

more source cubes In many

respects, a virtual cube is to

Analysis Server what a view

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There is no limit to the number of virtual cubes that can be defined in a database

Dimension Limitations

Following are limitations of virtual cubes:

! Virtual cubes cannot slice the dimensions of the source cubes For example,

suppose a source cube contains the dimension Region If Region is placed

in a virtual cube, the entire dimension is included You cannot include only

the Western region

! You cannot choose which levels of the dimension are included For example, you cannot include summary levels and exclude bottom-level members The entire dimension, with all levels, must be included

The Measures dimension is an exception to these rules You can pick the

specific measures that populate a virtual cube

Storage and Performance

Because virtual cubes consume no disk space, they rely on the underlying storage of the source cubes Therefore:

! A single virtual cube can include multidimensional OLAP (MOLAP), relational OLAP (ROLAP), and hybrid OLAP (HOLAP) source cubes

! Because a single source cube can contain MOLAP, ROLAP, and HOLAP partitions, there is endless flexibility in designing virtual cubes

Virtual cubes automatically use aggregations from the source cubes The performance overhead imposed by the virtual cube on top of the source cubes is negligible

4 Module 12: Working with Virtual Cubes

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Obtaining Logical Results

When building a virtual cube based on more than one source cube, you must follow some simple rules to obtain logical results

Common dimensions and measures are required from source cubes:

! The source cubes should contain one or more shared dimensions that are the same, and at least one of the common shared dimensions should be included

in the virtual cube

! Analysis Manager does not enforce this rule, but the result will be nonsensical if it is not followed This can be easily visualized from the preceding spreadsheet illustration The first cube contains region and time dimensions The second cube contains sales representatives and scenario dimensions Because the two cubes have nothing in common, it makes no sense to base a virtual cube on them

There is no analytical value in combining cubes if they do not share a dimension

! Include at least one measure from each source cube in the virtual cube or there is no reason to combine the cubes Again, Analysis Manager will not prevent you from doing this

Topic Objective

To explain the importance of

using common measures

and dimensions from the

source cubes

Lead-in

When building a virtual cube

based on more than one

source cube, you must

follow some simple rules to

obtain logical results

Delivery Tips

Explain the preceding

illustration by comparing two

cubes with different

dimensionality Combining

them into a virtual cube

would produce nonsensical

results

Note

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$ Building a Virtual Cube

! Choosing the Source Cubes

! Choosing the Measures

! Choosing the Dimensions

! Finalizing the Virtual Cube

You build a virtual cube simply by using the Virtual Cube Wizard To display

the wizard, right-click the Cubes folder and then click New Virtual Cube

Topic Objective

To go through the steps of

creating a virtual cube

Lead-in

To create a virtual cube, you

use the Virtual Cube

Wizard

6 Module 12: Working with Virtual Cubes

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Choosing the Source Cubes

At the first step of the Virtual Cube Wizard, select the source cube or cubes from which the virtual cube will be derived

Remember that if you select multiple source cubes, these cubes should have at least one shared dimension in common

To select a source cube, either click a cube from the Available cubes box and then click the arrow (>), or double-click the cube To select all the cubes, click the double arrow (>>) The names of the selected cubes appear in the Virtual

cube includes box To remove a cube from this list, either click the cube and

then click the back arrow (<), or double click the cube in the Virtual cube

includes box

Topic Objective

To show how to choose

source cubes for a virtual

cube

Lead-in

The first step in creating a

virtual cube is to select the

source cube or cubes for the

virtual cube

Delivery Tip

Enhance your lecture by

opening the Virtual Cube

Wizard and showing

students the corresponding

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Choosing the Measures

The next step is to add measures to the virtual cube The wizard displays the

measures from the selected source cube or cubes in the Available measures

box

Remember to include at least one measure from each source cube The

source cube name appears in the second column of the Available Measures

box

To select a measure, either click a measure from the Available measures box and then click the arrow (>), or double-click the measure To select all the measures, click the double arrow (>>) The names of the selected measures appear in the Selected measures box To remove a measure from this list, either click the measure and then click the back arrow (<), or double click the measure in the Selected measures box

Topic Objective

To show how to select

measures for a virtual cube

Lead-in

The next step is to add

measures to the virtual

8 Module 12: Working with Virtual Cubes

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Choosing the Dimensions

Next, choose the dimensions The wizard displays the dimensions from the

selected source cube or cubes in the Available dimensions box

If the virtual cube is based on more than one source cube, you must select

at least one shared dimension in common between the cubes to obtain a logical result

To select a dimension, either click a dimension from the Available dimensions box and then click the arrow (>) or double-click the dimension To select all the dimensions, click the double arrow (>>) The names of the selected dimensions appear in the Selected dimensions box To remove a dimension from this list, either click the dimension and then click the back arrow (<) or double-click the dimension in the Selected dimensions box

The list of dimensions includes all virtual dimensions defined in the source cubes A virtual dimension can be placed in a virtual cube The dimension from which it is derived will be placed in the virtual cube automatically You cannot include a virtual dimension in a virtual cube without also including the

dimension on which it is based

Topic Objective

To show how to choose

dimensions for a virtual

cube

Lead-in

The next step is to choose

the dimensions for the