What constellation is imskey _ieo?

The following describes the IMS hierarchical database:

Overview of information management system of international monitoring system

Data definition of IMS

The data definition of IMS includes database schema definition and external schema definition.

The database schema of IMS is a collection of physical database records. all

The record type of the database corresponds to the hierarchical mode in the hierarchical data model,

Defined by DBD. Mapping from physical database record type to storage database

The mapping is contained in the DBD definition of this physical database record type.

The external schema of IMS is a collection of logical database records. Each logical number

The database record type is defined by PCB. Logical database record type is

The mapping of IMS database schema is contained in this logical database record type.

PCB definition. Users manipulate data according to external mode.

The following respectively introduces the database schema definition and external schema definition:

1 database schema definition

2 external schema definition

Database schema definition

The database schema of IMS is a set of physical database records (PDBR type),

Each PDBR type is a hierarchical tree structure composed of several related fragment types.

Its root fragment value and one of its descendant fragment values constitute a value of PDBR type,

I.e. database records or instances.

Each PDBR type defines its logical structure and storage nodes through a DBD statement group.

The definition of IMS database schema is an arrangement of a set of DBD definitions.

In the process of DBD definition, the order of each fragment type determines the value of each fragment in the database.

, which will affect the execution results of some DL/ 1 statements. Ask for this

Hierarchical order of species sequence and fragment type in PDBR tree (from top to bottom, from left to right)

Be consistent.

PDBR (1) teaching database and examples.

② Definition of ②DBD to ②PDBR,

(3) 3) The code of each fragment type of PDBD type and the hierarchical sequence value of fragments.

External schema definition

The external schema is the local logical structure of the data needed by each user, which belongs to the application.

Data view generally involves only a part of the database, so it needs to be of PDBR type.

Define separately on the basis of. A database schema has several external schemas, and many external schemas are allowed.

Applications share an external mode, but each application can only start one external mode.

Type. An external schema is a set of logical database record types (LDBR types).

Write it as PSB. LDBR type is a subtree of PDBR type, which consists of PCB.

Definition.

The definition of external mode follows the following rules:

If an external mode contains a clip type, it must contain its parent clip type. '

The following explains how to define logical database record types.

LDBR model of (1) teaching database

(2) 2) Definition of LDBR PCB

Recording LDBR with PCB definition logical database

( 1)PCB type=DB，DBDname=TS，key length = 10

(2)SENSEG name=dept，PROCopt=G

(3)SENSEG name = course, parent = department, procopt = all.

(4)SENSEG name = student, parent = course, procopt = r.

The data operation language of IMS is DL/ 1.

Users use high-level languages (called host languages) to program,

Access to the database is realized by embedding DL/ 1 statement.

DL/ 1 command

Gu took out a fragment.

GN sequence to retrieve the next fragment.

GNP retrieves the next clip in the current parent clip.

And gu, ready to delete.

GHN, like GN, is ready to be deleted.

GHNP, like GUP, is ready to be deleted.

ISRT insertion fragment

REPL modifies fragment content

DELT deletes a clip and its descendants.

LOAD initially loads a fragment.

CHKP set up a checkpoint

SCHD plan PSB

$ TERM releases PSB

Storage structure of IMS

IMS provides four storage structures:

The following storage structure example is based on the teaching database PDBR.

1.HSAM: hierarchical sequential access method, in which fragments are stored in hierarchical order in physical adjacency.

2.HISAM: hierarchical index sequential access method,

Non-root segments are stored adjacently in ascending order of hierarchical order values,

The root fragment is organized by continuous domain indexes and points to subordinate areas.

3.HDAM: hierarchical direct access method, in which fragments are stored in a discrete distribution mode.

The root fragment is organized by the sequential domain hashing method, and the pointer is used from the root fragment.

Link physically dispersed dependent segments in the order of hierarchical order values.

4.HIDAM: hierarchical index direct access method, similar to HDAM, except that,

Root fragments are organized by sequential domain index technology instead of hash method.

Therefore, it is a mixture of HDAM and Hissam.

Root fragment in a fragment

HSAM sequential adjacency

HISAM index order adjacency

HDAM hash linked list

HIDAM index linked list