Changes in V4.2

The following describes the most significant changes which occurred in HDS between versions V4.1 and V4.2 (not the current version).

1. Support for the VAX/VMS operating system has been discontinued at this version of HDS and all references to VMS usage have been dropped from this document.

   A VAX/VMS implementation of HDS V4.1 remains in operation and continues to be supported by Starlink on a "care and maintenance" basis, but as a separate entity. This means that the following and future additions to HDS will not be applied to the VAX/VMS version. Users of HDS on VAX/VMS should refer to the documentation that accompanies it for information, and not to this document.

2. The OSF1 (Digital UNIX) implementation of HDS now supports file mapping. This should improve the performance of those applications that can take advantage of it.

3. HDS now allows container files that are marked for deletion to be re-opened for use, so long as they have not yet been closed (and therefore deleted). This facility was found to be necessary to support foreign data file access in the NDF library (SSN/20).

4. Due to the introduction of various new POSIX facilities on OSF1 (Digital UNIX) and associated compiler flags, some untested code was being compiled and used on this platform. The result was that file specifications containing "wild-carding" characters could not be used and the HDS_WILD routine did not function correctly in recent un-tested distributions of HDS for OSF1. These problems have now been fixed.

5. A bug has been fixed which meant that the HDS_WILD routine would not function correctly if it was the first HDS routine to be called in an HDS application. A call to HDS_START would prevent this problem occurring, but is now no longer necessary.

6. A bug has been fixed which could result in objects accessed for modification using file mapping to be written back to their container files using a write call (instead of unmapping the file) if the `MAP' tuning parameter was changed between calls to DAT_MAP (or equivalent) and DAT_ANNUL (or equivalent). This problem did not occur if DAT_UNMAP was called to unmap the data explicitly. Surprisingly, this erroneous behaviour almost always gave the correct result, but could very occasionally result in a core dump.

7. A bug has been fixed that could corrupt data in the immediate neighbourhood of a primitive object slice whose value was updated. This could only happen in rare circumstances and was normally limited to slices no more than 32 bytes in length.

8. Certain error messages that are often the result of an attempt to access a corrupt HDS container file have been modified to explicitly give the affected file name.

9. The HDS makefile has been extensively revised. Amongst other things, this is to permit automatic distribution via the Starlink Software Store on the World Wide Web.

10. This document (SUN/92) has been revised and is now available in both Latex and hypertext (HTML) forms.

11. The HDS implementations on SunOS and Ultrix systems have been superceded by Solaris and OSF1 implementations respectively (the latter now being called Digital UNIX). The code to support these (and other) earlier implementations of HDS has been retained, and may be of use to those wishing to port HDS back to these platforms. However, it is no longer supported on these systems by Starlink and has not recently been built or tested on them. An Open VMS implementation of HDS running on Dec Alpha workstations is also known to exist, but is not supported by Starlink.

    Further information about old or unsupported implementations of HDS may be obtained by contacting Starlink Software Support (stardev@jiscmail.ac.uk)