scope:

Introduction

The data structures used with SSI have remained remarkably stable since the changes made immediately after the pilot scheme at Leamington Spa, but minor developments in data, and associated changes to data compilers and decompilers, and to programs which process the data, whether in the target SSI systems or in SSI Design Workstation (DWS) Simulation Systems have led to a requirement for data compatibility checks. A small number of errors found in the above programs have resulted in constraints on data design, and thus further data compatibility checks are required to confirm these constraints are complied with.

Section 2 has a list which is used to establish which data compatibility checks, on a per Central Interlocking basis, have to be made during the data preparation and checking process. These checks are then detailed in the following Sections, together with any required data changes which may result. Background information is also included for each check. The Central Interlocking Status Record, (CISR) Part 6, is then used to record that these checks have been made.

Once these checks have been made, the data will be compatible with compilers and decompilers on the DWS and with the data-processing program issues that the data will be either tested with on the DWS Simulation System or tested or commissioned with in the target Interlocking. Testing of a particular Interlocking's data on the DWS (or on-site) has to be carried out using data-processing program issues that equate to those intended to be used in this Interlocking on-site when it is commissioned. Where the program issue is subsequently changed, then some retesting may be required to address any changes in data functionality or increases in data processing times.

Program changes in the backwards direction are banned unless site-specific specialised advice, approved by the Infrastructure Owner, is obtained and followed.

Data used in the pilot schemes (category 1A) with original programs (i.e. Leamington Spa, prior to its conversion, and concurrent South African schemes) is a special case and thus outside the scope of this document.

The integrity of these checks depends in part on the use of the CISR to record data Versions/Sub-versions, the associated SSI Design Workstation software issue and on-site program issues.