Compaq COBOL AAQ2G1FTK - Manual (Page 253)

8
Sharing Files and Locking Records
This chapter includes the following information about sharing files and protecting
records for sequential, relative, and indexed files:
• Controlling access to files and records (Section 8.1)
• Choosing X/Open standard or Compaq standard file sharing and record
locking (Section 8.2)
• Ensuring successful file sharing (Section 8.3)
• Using record locking to control access to records (Section 8.4)
8.1 Controlling Access to Files and Records
In a data manipulation environment where many users and programs access the
same data, file control must be applied to protect files from nonprivileged users,
to permit the desired degree of file sharing, and to preserve data integrity in the
files. For example, in Figure 8–1 many users and programs want to access data
found in FILE-A.
Figure 8–1 Multiple Access to a File
Access
Stream 3 Access
Stream 2 Access
Stream 1
PROG−A
User 3 User 2
PROG−B PROG−A
Location 3 Location 2
ZK−6323−GE
Location 1
User 1
FILE−A
Sharing Files and Locking Records 8–1