Common data model

The common data model (CDM) is the set of Configuration Item (CI) and relationship classes that ship with BMC Helix CMDB. These classes represent the physical, logical, and conceptual items of all IT environments that you want to track in a CMDB.

When you setup a CMDBfor your organization for the first time, use this diagram to understand the relationships between out-of-the-box classes and understand the inheritance of attributes from the parent classes to the child classes. 

To extend the data model and customize it to your business requirement, you must create your own classes or extend a class with additional attributes. See Modifying-the-data-model-by-using-Class-Manager.

Related topics

Key-concepts

Product-overview

Getting-started 

Managing-the-common-data-model

CDM diagram download page (login required)

The common data model of the BMC Helix CMDB unifies the representation of configuration data. It is designed to store data about the most common configuration items (CIs), such as hardware, software, and services. It helps link the CI information to provide a complete view of all elements in an IT environment and the way in which they affect each other.

For consistency with the industry standards that have been developed to track and manage this type of information, the CDM is based on the Common Information Model (CIM) from the Distributed Management Task Force (DMTF) and Microsoft Windows Management Instrumentation (WMI). The CDM adopted much of the basic design of the CIM and WMI without going into the same depth on the internal workings of systems.

Classes and attributes needed only by a specific BMC product are not part of the CDM. These extensions are installed by the product that consumes data from them and they reside in separate namespaces.

For information about the complete structure and class details of the CDM, see the BMC Helix CMDB CDM Diagram and the BMC Helix CMDB CDM Help in the PDFs-and-videos page.

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CIs and relationships

The CDM is composed of configuration items (almost always known as CIs) and relationships.

  • CIs are configurable things in an organization that must be managed to deliver an IT or business service. For example, a server in a data center or a software running on a computer. 
  • Relationships represent the connections between CIs. An instance of the relationship class will therefore relate an instance of the first or source CI class to an instance of the second or destination CI class. The two CIs are considered members of the relationship.


Relationship directionality

Relationships, like CIs, have attributes. Relationships have directionality that identifies the source and destination.

In the diagram, it is important to have the direction of the arrow pointed correctly. The arrowhead always points to the destination, and the reverse direction for a relationship cannot be assigned. For example, if two CIs, A and B, have a BMC_Dependency relationship, where A depends on B, then A is the Destination, and B is the Source. The arrow would point to A. That is, it would be drawn as A <- B. The reverse, A -> B, is never a possibility. If two CIs are interdependent, then those CIs are denoted with a bidirectional arrow.

For more information and examples, see Relationships-represented-in-a-data-model-diagram.

Sample data models using the CDM

The following figures illustrate the use of classes in the CDM to model your data. The boxes represent configuration item (CI) classes and the lines represent relationship classes. The models shown here are simplified and do not necessarily represent best practices.

Sample model for a computer system

The following figure illustrates a typical computer system data model. It has an operating system, a BIOS, a word-processing application, a video card, and uses a network printer.

Classes used for a computer system and components

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Sample model for a computer system in a LAN

The following figure illustrates a data model in which a computer system participates in a LAN. The computer system is in an IP subnet that is part of the LAN.

 Classes used for a computer system in a LAN

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