CHECK Rule

Overview of the CHECK Rule

Use the CHECK rule to instruct the GLASS engine to run each potential match through a specific algorithm as a form of validation to reduce or eliminate false positive matches. A location is only returned as a match if it passes the checksum module that is applied to the GLASS expression(s).

For example, apply the LUHNCHKSUM checksum module to validate the check digit for potential primary account number (PAN) matches.

The generic GLASS syntax for CHECK is:

<search pattern> CHECK '<checksum module>'

See Supported Check Modules for a list of common checksum modules that are built-in and ready to use in your custom data types.

CHECK Example 1

Your organization issues American Express (AMEX) corporate cards for employees who require it.

You develop a custom GLASS data type that searches for AMEX card numbers that are stored in plain text across your organization's storage locations, with the following requirements:

• All AMEX card numbers are 15 digits long.
• All AMEX card numbers must start with 34 or 37.
• AMEX card numbers are stored as 15 straight digits with no separators (e.g. hyphens -, whitespaces  ) and cannot be bounded by digits.
• The last digit in a valid AMEX card number must pass the Luhn formula for MOD-10 checksum.

MAP 'AMEX_PREFIX' 34, 37
(GROUP 'AMEX_PREFIX' THEN RANGE DIGIT TIMES 13) \
CHECK 'LUHNCHKSUM' BOUND NONDIGIT

Based on the GLASS expression above, the GLASS pattern matching engine will return Line 1 and Line 2 as match locations:

Line 3 and Line 4 will not be returned as match locations.

• For Line 3, part of the data pattern passed the LUHNCHKSUM checksum but failed the BOUND rule as it is surrounded by digits (9 and 3) on both sides.
• For Line 4, the data pattern passed the BOUND rule but failed the LUHNCHKSUM checksum due to an invalid check digit (9).

Example 1 in GLASS Studio Visual Builder Mode

The equivalent configuration in GLASS Studio Visual Builder mode is:

• Group label: AMEX_CARD_NUMBER
  • Data type component: LIST (GROUP)
    • Data pattern to search for (+ Create Map):
      • Label : AMEX_PREFIX
      • Entries: 34, 37
  • Data type component: RANGE
    • Data pattern to search for (Use Keyword): DIGIT
    • Repeat Character/Octet (TIMES) option: Checked, 13 times
  • Bound (BOUND) rule (Select a keyword): Non-Digit on the Left and Right.
  • Check (CHECK) algorithm: LUHNCHKSUM

CHECK Example 2

ACME Corporation's regional customer ID is a 12-digit string that starts with a supported 2-character ccTLD (<ccTLD>), followed by a 9-digit serial number (<9-digit serial number>), and a single check digit (<check digit>) that must pass the MOD-10 checksum algorithm adopted for use in Machine Readable Travel Documents (MRTDs).

To search for the regional customer ID, you write a custom data type as follows:

MAP NOCASE 'ACME_CUST_ID_CCTLD' 'AU', 'IE', 'KR', 'SG', 'UK', 'US'
MAP 'INVALID_SERIAL_NUM' 0

( \
  GROUP 'ACME_CUST_ID_CCTLD' THEN \
  RANGE DIGIT TIMES 9 EXCLUDE 'INVALID_SERIAL_NUM' THEN \
  RANGE DIGIT \
) CHECK 'PASSPORTMOD10' BOUND NONALNUM

The equivalent configuration in GLASS Studio Visual Builder mode is:

• Group label: ACME_CUST_ID_REGIONAL
  • Data type component: LIST (GROUP)
    • Data pattern to search for (+ Create Map):
      • Label : ACME_CUST_ID_CCTLD
      • Entries: 'AU', 'IE', 'KR', 'SG', 'UK', 'US'
  • Data type component: RANGE
    • Data pattern to search for (Select a keyword): DIGIT
    • Repeat Character/Octet (TIMES) option: Checked, 9 times
    • Exclude (EXCLUDE) rule:
      • MAP Label: INVALID_SERIAL_NUM
      • MAP Entries: 0
  • Data type component: RANGE
    • Data pattern to search for (Use Keyword): DIGIT
  • Bound (BOUND) rule (Select a keyword): Non-Alnum on the Left and Right.
  • Check (CHECK) algorithm: PASSPORTMOD10

Supported Check Modules

The following is a list of all built-in checksum modules that are defined in the GLASS language and can be applied to your custom GLASS expressions.

Adding CHECK Rules

To add a CHECK rule for a base pattern in GLASS Studio Visual Builder Mode:

1. Add and define the data pattern for a RANGE, WORD, or LIST component.
2. In the Add Pattern Rules pane, click on Check.
   
3. Select the checksum algorithm(s) from the list of built-in check modules.
4. (Optional) Click to remove a selected checksum algorithm from the CHECK rule.
5. Click Close.

Managing CHECK Rules

To edit a CHECK rule:

1. Left click anywhere in the component to open the base pattern form.
2. Click on the Down icon next to the CHECK panel.
3. Add (check) / remove (uncheck) the selected checksum algorithms.
4. Click Close.

To remove a CHECK rule:

1. Left click anywhere in the component to open the base pattern form.
2. Click on the Trash icon next to the CHECK panel.
   
3. Click Close.