CMDB Data Model Design

The configuration management database needs to be able to store records for every configuration item and relationship in the systems it supports.  The storage requirements for these systems may differ.  For example, the properties of a  network switch are different to the ones for a database.  The structure of configuration item records will also differ. This can be a problem when you decide to store configuration item records in a database.  It is difficult to design a database schema that is able to record metadata for a diverse range of configuration items.

One way around this is to incorporate XML Type columns into the design.  The diagram below shows an example of this.  It has 3 tables: CMDB_ITEMS, CMDB_RELATIONSHIPS and CMDB_TYPES.  CMDB_ITEMS and CMDB_RELATIONSHIPS are arranged in a bill of materials structure.  

CMDB data model diagram

CMDB_ITEMS stores configuration item records.  Each record has a system generated id along with a name, version and type id.  The name, version and type combination form an unique constraint for the table.  The configuration record is stored as an XML document in the XRECORD column.  An MD5 hash value is created for the XRECORD.  This can be used to help identify configuration items that exist in more than one configuration. 

CMDB_RELATIONSHIPS stores the relationships between configuration item records.  It uses the source and target configuration item ids in conjunction with the relationship type to identify the relationship.  An XML Type column in CMDB_RELATIONSHIPS can be used to store XML documents that include data to describe the relationship.

CMDB_TYPES stores metadata that describes configuration items and relationships.  Each type has a system generated id and a unique name + version.  The RECORD_SCHEMA column stores an XML schema that can be used to validate the structure of the item or relationship XML documents.


Records configuration items

Name Datatype Length Mandatory Comments
CIID NUMBER (38) Yes System generated configuration item ID
NAME VARCHAR2 (256) Yes Configuration item name
VERSION VARCHAR2 (64) Yes Configuration item version
TYPE_ID NUMBER (38) Yes Configuration item type - foreign key to CMDB_TYPES
MD5_HASH VARCHAR2 (256) No MD5 Hash of the configuration item record.
XRECORD XMLTYPE CLOB No Configuration item record stored in XML format.


Records relationships between configuration items

Name Datatype Length Mandatory Comments
SOURCE_CIID NUMBER (38) Yes Source configuration item ID - foreign key to CMDB_ITEMS
TARGET_CIID NUMBER (38) Yes Target configuration item ID - foreign key to CMDB_ITEMS
TYPE_ID NUMBER (38) Yes Relation type ID - foreign key to CMDB_TYPES
XRECORD XMLTYPE CLOB No Configuration item relationship record


Records metadata for the CMDB_ITEMS and CMDB_RELATIONSHIP tables

Name Datatype Length Mandatory Comments
TYPE_ID NUMBER (38) Yes System generated primary key
NAME VARCHAR2 (256) Yes A name to identify the CMDB type.
VERSION VARCHAR2 (64) Yes CMDB type version
RECORD_SCHEMA XMLTYPE CLOB No An XML Schema that can be used to validate item and relationship instance documents