X/Open group (also known as theOpen Group for Unix Systems[1][2] and incorporated in 1987 asX/Open Company, Ltd.[3][4]) was aconsortium founded by several EuropeanUNIX systems manufacturers in 1984[3][5] to identify and promoteopen standards in the field ofinformation technology. More specifically, the original aim was to define a single specification foroperating systems derived from UNIX, to increase the interoperability of applications and reduce the cost of porting software. Its original members wereBull,ICL,Siemens,Olivetti, andNixdorf—a group sometimes referred to asBISON.[6]Philips andEricsson joined in 1985,[6] at which point the name X/Open was adopted.
The group published its specifications asX/Open Portability Guide, starting with Issue 1 in 1985, and later asX/Open CAE Specification.
In 1987, X/Open was incorporated as X/Open Company, Ltd.[3][4]
X/Open published its specifications under the name X/Open Portability Guide (or XPG). Based on the AT&TSystem V Interface Definition,[13] the guide has a wider scope thanPOSIX, which is only concerned with direct operating system interfaces. The guide specifies aCommon Application Environment (CAE) intended to allow portability of applications across operating systems. The primary aim was compatibility between different vendors' implementations ofUNIX, though some vendors also implemented the standards on non-UNIX platforms.
Issue 1 of the guide covered basic operating system interfaces, the C language, COBOL, indexed sequential file access method (ISAM) and other parts[14] and was published in 1985.[15] Issue 2 followed in 1987,[15] and extended the coverage to include Internationalization, Terminal Interfaces, Inter-Process Communication, and the programming languagesC,COBOL,FORTRAN, andPascal, as well as data access interfaces for SQL and ISAM.[16] In many cases these were profiles of existing international standards. Issue 3 (XPG3) followed in 1989,[15] its primary focus being convergence with thePOSIX operating system specifications; it added Window Manager, ADA Language and more.[17] Issue 4 (XPG4) was published in July 1992. TheSingle UNIX Specification was based on the XPG4 standard. The XPG3 and XPG4 standards define all aspects of the operating system, programming languages and protocols which compliant systems should have.
Multiple levels of compliance and corresponding labels were available, depending on the scope of the guide that was covered: Base and Plus; labels Component and Application are for SW components and applications that make use of the portability guide.[18]
Issue 1 was published as a single publication with multiple parts,ISBN0-444-87839-4.
Issue 2 was published in multiple volumes:
X/Open Portability Guide Volume 1: System V Specification Commands and Utilities, 1987,ISBN0-444-70174-5
X/Open Portability Guide Volume 2: System V Specification System Calls and Libraries, 1987,ISBN0-444-70175-3
X/Open Portability Guide Volume 3: System V Specification Supplementary Definitions, 1987,ISBN0-444-70176-1
System Interface Definitions (XBD), Issue 4, 1992,ISBN1-872630-46-4, C204
The above three documents were published not under the labelX/Open Portability Guide but rather asCAE Specification.[15]Nonetheless, the termX/Open Portability Guide, Issue 4 sees some use in reference to 1992 year of publication.[19][20]
Further X/Open publications under the labelX/Open CAE Specification rather thanX/Open Portability Guide:
Distributed Transaction Processing: The XA Specification, December 1991,ISBN1-872630-24-3[21]
Systems Management: Management Protocol Profiles (XMPP), October 1993,ISBN1-85912-018-0[22]
^Pasquali, Virgilio (Summer 2005)."ICL and Europe".Resurrection: The Bulletin of the Computer Conservation Society (35).ISSN0958-7403. Contains more on history of X/Open.
