Introduction

In this section:

SCAN vs. MODIFY, MAINTAIN, HLI, and FSCAN

SCAN permits you to:

Add records to new or existing FOCUS or XFOCUS databases.
Change field values in FOCUS databases. With SCAN, you can change the values in KEY fields (not possible with MODIFY requests).
Delete records from FOCUS databases.
Search through FOCUS databases to locate instances of specified character strings or values.
Display complete record contents showing all field values, or subsets of the fields in FOCUS databases.
Move (relink) record segments and descendant segments from one parent record to another in FOCUS databases with parent-descendant structures.

In a typical SCAN session you identify a database and locate specific logical records of interest. Your knowledge of the database's structure and contents allows you to navigate from field to field. Within the database you can add or delete instances of data at the segment level or change data values at the field level.

Note: On databases protected with DBA passwords, SCAN is only available to those who have the proper password.

As you work in a SCAN session, your changes are accumulated in a revised version of your original database. When you decide to terminate your session, you can either save the changed version of the database and overwrite the original version with it, or keep the original version as it was when you started (if you have inadvertently changed the database).

We recommend that you copy your databases before using SCAN as an additional safety precaution; SCAN is a powerful tool for manipulating data, but keeps no log of the change transactions. Using the FOCUS Absolute File Integrity feature (SET SHADOW=ON) protects you against loss of data due to system crashes. (The SET SHADOW command is only effective if it has been issued prior to database creation. Consult the Describing Data manual for information about the Absolute File Integrity feature. See the Developing Applications manual for more information about SET parameters.)

Note: Absolute File Integrity and shadow paging are not supported for XFOCUS data sources.

SCAN vs. MODIFY, MAINTAIN, HLI, and FSCAN

FOCUS includes five facilities for maintaining the data in FOCUS databases. You should be aware of their differences:

The SCAN facility is useful for examining the data in FOCUS databases to review or physically add, change, or delete data fields. With SCAN, an experienced user can quickly adjust database contents to correct errors or update fields. To use it effectively, however, you must know the database's contents and structure.
Caution: Because SCAN works directly on the data, there is the potential for corrupting data if you are unsure of the nature of your database. For example, if a SCAN operation such as REPLACE is issued against a database field such as SALES, without adequate selection criteria, every legitimate SALES field in the database could be overwritten by the replacement value, and all field values would have to be reentered.
MODIFY (see Modifying Data Sources With MODIFY) is a transaction processing environment that is used for maintaining FOCUS databases. MODIFY requests can be developed with elaborate match logic and data validation, as well as transaction logging. Such procedures, when fully tested, can be run by clerical personnel with no threat to database security.
HLI (Host Language Interface) is an optional interface. It allows you to read and edit FOCUS databases from programs written in other programming languages (FORTRAN and C). HLI is similar to SCAN in function. HLI is described in the Host Language Interface manual.
The FSCAN facility (see Directly Editing FOCUS Databases With FSCAN) is similar to the SCAN facility: You can view, add, change, or delete data in your FOCUS databases. The FSCAN facility provides full-screen capabilities such as a prefix area and a command line. It also provides confirmation screens for DELETE and QUIT operations. Unlike SCAN, the FSCAN facility displays parent instances that lack descendant instances (short path records) and verifies acceptable test values defined with ACCEPT parameters. MARK and MOVE subcommands are not supported.