The document introduces the basic concepts of IMS databases, including databases, IMS databases, hierarchical structures, segment rules, segment relationships, hierarchical sequential access, segment storage organization, sequential organization, HSAM, HSAM storage, HSAM processing, SHSAM, HISAM, HISAM storage, HISAM VSAM logical records, HISAM inserts, insert root 4, insert root 5, insert dependents, G22 and D24 HISAM delete and replace, SHISAM, GSAM, etc.