ISO 8583 schemas: Overview and structure

HCL OneTest™ API supports the ISO 8583 standard for messages that originate in financial transaction cards.
ISO 8583 schemas typically require you to modify them before you apply them to a message. HCL OneTest API includes sample schema files, which you can use as a basis for your own schemas, in the following location:
ISO 8583 messages can be preceded by a customized header, but the core layout always contains the following sections:
The Message type indicator (MTI) section consists of four numeric digits:
  • MTI_Version (1987, 1993, or 2003)
  • MTI_MessageClass
  • MTI_MessageFunction
  • MTI_MessageOrigin
One or more bitmaps
A message always has an 8-byte primary bitmap whose individual bits indicate which later fields are present in this particular message instance. The primary bitmap specifies whether fields 1 - 64 are present. If a secondary bitmap is also included, it specifies whether fields 65 - 128 exist. The standard also provides for a tertiary bitmap, but this option is rarely used.
When you edit an ISO 8583 message, you are not required to touch these bitmaps. Delete the fields from the message that you do not use, and HCL OneTest API updates the appropriate bitmap for you.
Message data fields
Data fields as defined in the ISO 8583 specification, containing information about the transaction, such as amounts, dates, times, and country codes. For example, the second field is PrimaryAccountNumber_002, with a default data type of Type_n_LL, indicating a two-digit numeric field.
Change the data type for any of these fields only when you use the schema for non-standard business-to-business transactions between parties who have the same modifications to the schema.