The 1997 ASOC has a three level structure. The division is the broadest level and has a two-digit code (e.g. 01), the subdivision is the intermediate level and has a three-digit code (e.g. 011) and the group is the most detailed level and has a four-digit code (e.g. 0111).
The main purpose of divisions is to provide a limited number of categories which represent broad groups of criminal offences suitable for publication of summary statistics. There are 16 divisions within the ASOC with the codes numbered 01 to 16.
The subdivision and group levels provide increasingly detailed dissections of these broad categories.
The three-digit code structure that represents the 46 subdivisions ranges from 011 to 169. There are many unused numbers within this range, which provides scope for expansion of the classification structure in future editions. Subdivision codes are created by appending a digit between 1 and 9 to the two-digit division code to which they are linked. No division has more than 5 subdivisions, although the code structure provides for up to 9, no subdivision code ends in zero and all subdivision codes ending in 9 are 'Other' or residual categories, that is they represent categories which are clearly a part of the broader division but can not be included in any of the other specified subdivisions.
The four-digit code structure that represents the 120 groups ranges from 0111 to 1699. There are again many gaps within this range. As with the subdivisions this provides scope for expansion of the classification structure in future editions. Group codes are created by appending a digit between 1 and 9 to the three-digit subdivision code to which they are linked. No subdivision has more than 7 groups, although the code structure provides for up to 9, no group code ends in zero and all group codes ending in 9 are 'nec' (not elsewhere classified) or residual categories, that is they represent categories which are clearly a part of the broader subdivision but can not be included in any of the other specified groups.
The structure of the classification does not contain any seriousness hierarchy and classification codes cannot and should not be used as an index of seriousness.
When the data provided are inadequate to allow a four-digit group to be allocated a Supplementary code may be applied. Supplementary codes may be generated by taking a three-digit subdivision code and adding a single zero to it to make a four-digit code.
In any instances where a subdivision cannot be selected, the most suitable division is selected and two zeros are appended to its code to make a four-digit code.
There are two further Supplementary codes that may be used, but only if the situation explicitly warrants it. If the data provided cannot be assigned to any ASOC division, and there is no provision for contacting the data provider, then the four-digit code of 9999 can be used. If no data at all are provided, and again there is no provision for contacting the data provider, then the four-digit code of 9998 can be used.
A full listing of these Supplementary codes and their titles is provided at the end of the classification structure.