Distributed Computing Environment: Difference between revisions

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{{more citations needed|date=December 2011}}

The '''Distributed Computing Environment''' ('''DCE''') wasis a [[software system]] developed in the early 1990s from the work of the [[Open Software Foundation]] (OSF), a consortium founded in 1988 that included [[Apollo Computer]] (part of [[Hewlett-Packard]] from 1989), [[IBM]], [[Digital Equipment Corporation]], and others.<ref name="JiaZhou2004">{{cite book|author1=Weijia Jia|author2=Wanlei Zhou|title=Distributed Network Systems: From Concepts to Implementations|url=https://books.google.com/books?id=_pYyEgj0fX8C&pg=PA135|date=15 December 2004|publisher=Springer Science & Business Media|isbn=978-0-387-23839-5|page=135}}</ref><ref name="SINHA1998">{{cite book|author=PRADEEP K. SINHA|title=DISTRIBUTED OPERATING SYSTEMS: CONCEPTS AND DESIGN|url=https://books.google.com/books?id=SewHKWac2I4C&pg=PA35|date=1 January 1998|publisher=PHI Learning Pvt. Ltd.|isbn=978-81-203-1380-4|page=35}}</ref> The DCE supplies a [[software framework|framework]] and a toolkit for developing [[client/server]] applications.<ref name="Jacobsen2003">{{cite book|author=Hans-Arno Jacobsen|title=Distributed Infrastructure Support for Electronic Commerce Applications|url=https://books.google.com/books?id=9W8QkfzD0VYC&pg=PA14|date=30 November 2003|publisher=Springer Science & Business Media|isbn=978-1-4020-7648-0|page=14}}</ref> The framework includes:

* a [[remote procedure call]] (RPC) mechanism known as [[DCE/RPC]]

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* an [[authentication]] service

* a [[distributed file system]] (DFS) known as [[DCE Distributed File System|DCE/DFS]]

The DCE did not achieve commercial success.

DCE represented a big step in the direction of standardization of [[software architecture|architecture]]s, which had previously been manufacturer-dependent. Like the [[OSI model]], DCE has not seen much success in practical implementation; however, its underlying concepts have had more substantial influence over subsequent efforts.

==History==

As part of the formation of OSF, various members contributed many of their ongoing research projects as well as their commercial products. For example, HP/Apollo contributed its Network Computing Environment (NCS) and CMA Threads products. Siemens Nixdorf contributed its X.500 server and ASN/1 compiler tools. At the time, network computing was quite popular, and many of the companies involved were working on similar [[Remote procedure call|RPC]]-based systems. By integrating security, RPC and other distributed services on a single "official" distributed computing environment, OSF could offer a major advantage over SVR4, allowing any DCE-supporting system (namely OSF/1) to interoperate in a larger network.

[[Open Software Foundation]] (OSF) came about to a large degree as part of the [[Unix wars]] of the 1980s. After [[Sun Microsystems]] and [[AT&T Corporation]] worked together to produce [[UNIX System V|UNIX System V Release 4]] (SVR4) and refused to commit to fair and open licensing of Unix source code, many of the other Unix vendors felt their own market opportunities were unduly disadvantaged. The Distributed Computing Environment is a component of the [[OSF/1|OSF]] offerings, along with Motif, OSF/1 and the Distributed Management Environment (DME).

As part of the formation of OSF, various members contributed many of their ongoing research projects as well as their commercial products. For example, HP/Apollo contributed its Network Computing Environment (NCS) and CMA Threads products. Siemens Nixdorf contributed its X.500 server and ASN/1 compiler tools. At the time, network computing was quite popular, and many of the companies involved were working on similar [[Remote procedure call|RPC]]-based systems. By integrating security, RPC and other distributed services on a single "official" distributed computing environment, OSF could offer a major advantage over SVR4, allowing any DCE-supporting system (namely OSF/1) to interoperate in a larger network.

The DCE system was, to a large degree, based on independent developments made by each of the partners. [[DCE/RPC]] was derived from the ''[[Network Computing System]]'' (NCS) created at [[Apollo Computer]]. The naming service was derived from work done at Digital. DCE/DFS was based on the [[Andrew File System]] (AFS) originally developed at [[Carnegie Mellon University]]. The authentication system was based on [[Kerberos (protocol)|Kerberos]], and the authorization system based on [[Access Control List]]s (ACLs). By combining these features, DCE offers a fairly complete [[C (programming language)|C]]-based system for network computing. Any machine on the network can authenticate its users, gain access to resources, and then call them remotely using a single integrated [[Application Programming Interface|API]].

The rise of the [[Internet]], [[Java (programming language)|Java]] and [[web services]] stole much of DCE's [[mindshare]] through the mid-to-late 1990s, and competing systems such as [[CORBA]] muddied the watersappeared as well.

One of the major uses of DCE today is [[Microsoft]]'s [[Distributed Component Object Model|DCOM]] and [[ODBC]] systems, which use DCE/RPC (in [[MSRPC]]) as their network transport layer.{{Cn|date=December 2023}}

OSF and its projects eventually became part of [[The Open Group]], which released DCE 1.2.2 under a [[free software license]] (the [[GNU Lesser General Public License|LGPL]]) on 12 January 2005. DCE 1.1 was available much earlier under the OSF BSD license, and resulted in [[FreeDCE]] being available since 2000. FreeDCE contains an implementation of DCOM.

One of the major implementationssystems built on top of DCE was [[Encina (software)|Encina]], originally developed by [[Transarc]] (who werelater acquired by [[IBM]]). IBM used Encina as a foundation to port its primary mainframe transaction processing system ([[CICS]]) to non-mainframe platforms, as [[IBM TXSeries]]. (However, later versions of TXSeries have removed the Encina component.)

==Architecture==

The largest unit of management in DCE is a '''cell'''. The highest privileges within a cell are assigned to a role called ''cell administrator'', normally assigned to the "user" ''cell_admin''. Note that this need not be a real OS-level user. The cell_admin has all privileges over all DCE resources within the cell. Privileges can be awarded to or removed from the following categories : user_obj, group_obj, other_obj, any_other for any given DCE resource. The first three correspond to the owner, group member, and any other DCE principal respectively. The last group contains any non-DCE principal. Multiple cells can be configured to communicate and share resources with each other. All principals from external cells are treated as "foreign" users and privileges can be awarded or removed accordingly. In addition to this, specific users or groups can be assigned privileges on any DCE resource, something which is not possible with the traditional UNIX filesystem, which lacks ACL's.

Major components of DCE within every cell are:

#The '''Security Server''' that is responsible for authentication

#The '''Cell Directory Server''' (CDS) that is the repository of resources and ACLs and

#The '''Distributed Time Server''' that provides an accurate clock for proper functioning of the entire cell

Modern DCE implementations such as IBM's are fully capable of interoperating with Kerberos as the security server, LDAP for the CDS and the [[Network Time Protocol]] implementations for the time server.

While it is possible to implement a distributed file system using the DCE underpinnings by adding filenames to the CDS and defining the appropriate ACLs on them, this is not user-friendly. DCE/DFS is a DCE-based application which provides a distributed filesystem on DCE. DCE/DFS can support replicas of a fileset (the DCE/DFS equivalent of a filesystem) on multiple DFS servers - there is one read-write copy and zero or more read only copies. Replication is supported between the read-write and the read-only copies. In addition, DCE/DFS also supports what are called "backup" filesets, which if defined for a fileset are capable of storing a version of the fileset as it was prior to the last replication.

DCE/DFS is believed to be the world's only distributed filesystem that correctly implements the full POSIX filesystem semantics, including byte range locking. DCE/DFS was sufficiently reliable and stable to be utilised by [[IBM]] to run the back-end filesystem for the 1996 [[Olympics]] web site, seamlessly and automatically distributed and edited worldwide in different time zones.