Joel has released a swathe of articles covering this,
https://www-secure.symantec.com/connect/articles/inventory-database-schema-75-part-1-basic-inventory
https://www-secure.symantec.com/connect/articles/inventory-database-schema-75-part-2-hardware
https://www-secure.symantec.com/connect/articles/inventory-database-schema-75-part-3-operation-system
https://www-secure.symantec.com/connect/articles/inventory-database-schema-75-part-4-software-and-user
https://www-secure.symantec.com/connect/articles/inventory-database-schema-75-part-5-network-devices
https://www-secure.symantec.com/connect/articles/inventory-database-schema-75-part-6-inventory-pack-servers-virtual-machine-data
https://www-secure.symantec.com/connect/articles/inventory-database-schema-75-part-7-inventory-pack-servers-database-and-web