Home > Articles > Data

UDM: Linking Relational and Multidimensional Databases

This chapter is from the book


  • Unified Dimensional Model (UDM)

The Unified Dimensional Model (UDM) of Microsoft SQL Server Analysis Services 2005 makes it possible for you to set up your system so that different types of client applications can access data from both the relational and the multidimensional databases in your data warehouse, without using separate models for each.

It's been a common industry practice for some time now to build data warehouses that include a relational database for storing data and a multidimensional database for analyzing data. This practice developed because the large volumes of data that multidimensional databases were developed to analyze are typically stored in relational databases. The data would be moved to the multidimensional database for analysis, but relational database would continue to serve as primary storage.

Thus, it makes sense that the interaction between the stored data and the multidimensional database where it can be analyzed has been an important component of multidimensional database architecture. Our goal for Analysis Services 2005, put simply, is speedy analysis of the most up-to-date data possible.

The speedy and up-to-date parts are what present the challenge. The data in OLTP systems is constantly being updated. But we wouldn't want to pour data directly from an OLTP system into a multidimensional database because OLTP data is easily polluted by incomplete transactions or incomplete data entered in a transaction. In addition, you don't want your analysis engine to access the OLTP data directly because that could disrupt work and reduce productivity.

In a data warehouse, OLTP data is typically transformed and stored in a relational database and then loaded into a multidimensional database for analysis. To connect the two databases, you can choose from three methods, each one employing a different kind of interaction:

  • Relational systems (ROLAP), in which no data is stored directly in the multidimensional database. It is loaded from the relational database when it is needed.
  • Multidimensional systems (MOLAP), in which data is loaded into the multidimensional database and cached there. Future queries are run against the cached data.
  • Hybrid systems (HOLAP), in which the aggregated data is cached in the multidimensional database. When the need arises for more detailed information, that data is loaded from the relational database.

In earlier versions of Analysis Services, the multidimensional part of the data warehouse was a passive consumer of data from the relational database, restricted to whatever structures the relational database contained. The functions of storing data and analyzing data were not only separate, but you had to understand two models—one for accessing a relational database and one for accessing a multidimensional database.

Some client applications would use one model and others would use the other model. For example, reporting applications traditionally would access the data in a relational database. On the other hand, an analysis application that has to look at the data in many different ways would probably access the data in the multidimensional database, which is designed specifically for that sort of use.

Now, the UDM offers a substantially redefined structure and architecture so that the one model (UDM) serves the purposes of any client application. You no longer have to understand two models; we're providing a unified model. You can see, in Figure 3.1, how many different client applications can use UDM to access data in a variety of different data stores.

Figure 3.1

Figure 3.1 The UDM provides a unified model for accessing and loading data from varied data sources.

Analysis Services uses proactive caching to ensure that the user of the client application is always working with predictable data latency. In essence, proactive caching is a mechanism by which the user can schedule switching from one connection mode (ROLAP, MOLAP, or HOLAP) to another. For example, the user might set his system to switch from MOLAP to ROLAP if the data in the MOLAP system is older than, say, four hours.

UDM owes its flexibility to the expanded role of dimension attributes in Analysis Services 2005. (For more information about dimension attributes, see Chapter 6, "Dimensions in the Conceptual Model.") Because of this expanded role of attributes in dimensions, you can base your UDM on the logic of your business functions instead of the logic of your database. With this flexibility, the UDM produces data that is considerably more informative than the relational model—and more understandable to the user.

With UDM at the center of the multidimensional model, you no longer need to have different methods of data access for different data sources. Before UDM, every system had a number of specialized data stores, each one containing data that was stored there for a limited number of users. Each of these data sources would likely require specific methods of data access for loading data into the multidimensional model. With Analysis Services 2005 all the data of the enterprise is available through the UDM, even if those data sources are located on different types of hardware running different operating systems or different database systems. OLAP now serves as an intermediate system to guarantee effective access to the data.

More detailed information about UDM is spread across the chapters of Part II, "Creating Multidimensional Models"; Part IV, "Creating a Data Warehouse"; Part V, "Bringing Data into Analysis Services"; and Part VI, "Analysis Services Architecture."


UDM makes it possible to set up a system so that different types of client applications can access data from both the relational and the multidimensional databases. With UDM at the center of the multidimensional model, you no longer need to have different methods of data access for different data sources. UDM offers a substantially redefined structure and architecture so that one model (UDM) serves the purposes of any client application. The expanded role of dimension attributes in Analysis Services 2005 makes possible the flexibility of UDM.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020