symbian 2.3 Extensibility Due to the effort and potential disruption involved in changing file formats,the SIS format is designed to be extensible,and uses a type-length-value (TLV)format.Since each SIsField has a specified length when parsing a SIS file the installer will ignore fields with unknown types. 2.4 Compression The new SIS file format supports the compression of each of the files in the SIS file individually,and the SIscontroller can also be compressed.This reduces the extra space needed to carry out 2.5 Nesting rejecte 2.6 Supporting the re-signing of a SIS file file. Svmbian File Header SISContents SISController SISSignatures SISData 2.7 Programming Considerations 2.7.1 File Format format it is possible to construct a C++class with just the data from the SISField. www.symbian.com 4 2.3 Extensibility Due to the effort and potential disruption involved in changing file formats, the SIS format is designed to be extensible, and uses a type-length-value (TLV) format. Since each SISField has a specified length, when parsing a SIS file the installer will ignore fields with unknown types. 2.4 Compression The new SIS file format supports the compression of each of the files in the SIS file individually, and the SISController can also be compressed. This reduces the extra space needed to carry out installation. Compression is supported by using a SISCompressed SISField which can contain another compressed SISField inside. 2.5 Nesting In order to limit the amount of resource required to install a SIS file package, the installer will now only processes the nesting of SIS files down to a depth of 8. SIS files containing embedding to a greater depth than this will be rejected. 2.6 Supporting the re-signing of a SIS file Since the SIS file format has no offsets which need to be changed it is easy to add a new signature and certificate chains to the end of the meta-data of the SIS file, even though they are in the middle of the file. SISController ….. ….. ….. SISSignatures SISData ….. SISContents ….. Symbian File Header The SISSignatures SISField will be lengthened by the addition of additional signatures and certificate chains, and the SISFields following will be moved to a position further on in the file. 2.7 Programming Considerations 2.7.1 File Format The SIS file format is designed so that each type of SISField is represented by one class. This makes it easy to construct a C++ class instance from a SISField. Since there are no offsets used in the file format it is possible to construct a C++ class with just the data from the SISField