External Data Representation - AbsoluteAstronomy.com

External Data Representation (XDR) is a standard data serialization format, for uses such as computer network

Computer network

A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....

protocols. It allows data to be transferred between different kinds of computer systems. Converting from the local representation to XDR is called encoding. Converting from XDR to the local representation is called decoding. XDR is implemented as a software library of functions which is portable between different operating system

Operating system

An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

s and is also independent of the transport layer

Transport layer

In computer networking, the transport layer or layer 4 provides end-to-end communication services for applications within a layered architecture of network components and protocols...

.

XDR uses a base unit of 4 bytes, serialized in big-endian order; smaller data types still occupy four bytes each after encoding. Variable-length types like string and opaque are padded to a total divisible by four bytes. Floating-point numbers are represented in IEEE 754 format.

History

XDR was developed in the mid 1980s at Sun Microsystems

Sun Microsystems

Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...

, and first widely published in 1987.
XDR became an IETF standard

Internet standard

In computer network engineering, an Internet Standard is a normative specification of a technology or methodology applicable to the Internet. Internet Standards are created and published by the Internet Engineering Task Force .-Overview:...

in 1995.

The XDR data format is in use by many systems, including:

Network File System (protocol)
NDMP
NDMP
NDMP, or Network Data Management Protocol, is a protocol invented by the NetApp and Legato companies, meant to transport data between NAS devices and backup devices...

Network Data Managerment Protocol
Open Network Computing Remote Procedure Call
Open Network Computing Remote Procedure Call
Open Network Computing Remote Procedure Call is a widely deployed remote procedure call system. ONC was originally developed by Sun Microsystems as part of their Network File System project, and is sometimes referred to as Sun ONC or Sun RPC...
Legato NetWorker backup software (later sold by EMC)
NetCDF
NetCDF
NetCDF is a set of software libraries and self-describing, machine-independent data formats that support the creation, access, and sharing of array-oriented scientific data. The project homepage is hosted by the Unidata program at the University Corporation for Atmospheric Research...

(a scientific data format)
The R language and environment for statistical computing
High Level Architecture (simulation)
The HTTP-NG Binary Wire Protocol
The SpiderMonkey JavaScript engine, to serialize/deserialize compiled JavaScript code
The Ganglia
Ganglia (software)
Ganglia is a scalable distributed system monitor tool for high-performance computing systems such as clusters and grids. It allows the user to remotely view live or historical statistics for all machines that are being monitored.-Ganglia:It is based on a hierarchical design targeted at...

distributed monitoring system
The sFlow
SFlow
sFlow is a technology for monitoring network, wireless andhost devices.The sFlow.org consortium is the authoritative source for the sFlow protocol specifications: previous version of sFlow, including RFC 3176, have been deprecated.- Operation :...

network monitoring standard
The libvirt
Libvirt
libvirt is an open source API, daemon and management tool for managing platform virtualization. It can be used to manage Linux KVM, Xen, VMware ESX and other virtualization technologies...

virtualization library, API
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...

and UI
User interface
The user interface, in the industrial design field of human–machine interaction, is the space where interaction between humans and machines occurs. The goal of interaction between a human and a machine at the user interface is effective operation and control of the machine, and feedback from the...
The Firebird (database server)
Firebird (database server)
Firebird is an open source SQL relational database management system that runs on Linux, Windows, and a variety of Unix. The database forked from Borland's open source edition of InterBase in 2000, but since Firebird 1.5 the code has been largely rewritten ....

for Remote Binary Wire Protocol

XDR data types

boolean
Boolean datatype
In computer science, the Boolean or logical data type is a data type, having two values , intended to represent the truth values of logic and Boolean algebra...
int – 32-bit integer
Integer (computer science)
In computer science, an integer is a datum of integral data type, a data type which represents some finite subset of the mathematical integers. Integral data types may be of different sizes and may or may not be allowed to contain negative values....
unsigned int – unsigned 32-bit integer
Integer (computer science)
In computer science, an integer is a datum of integral data type, a data type which represents some finite subset of the mathematical integers. Integral data types may be of different sizes and may or may not be allowed to contain negative values....
hyper – 64-bit integer
Integer (computer science)
In computer science, an integer is a datum of integral data type, a data type which represents some finite subset of the mathematical integers. Integral data types may be of different sizes and may or may not be allowed to contain negative values....
unsigned hyper – unsigned 64-bit integer
Integer (computer science)
In computer science, an integer is a datum of integral data type, a data type which represents some finite subset of the mathematical integers. Integral data types may be of different sizes and may or may not be allowed to contain negative values....
IEEE float
Floating point
In computing, floating point describes a method of representing real numbers in a way that can support a wide range of values. Numbers are, in general, represented approximately to a fixed number of significant digits and scaled using an exponent. The base for the scaling is normally 2, 10 or 16...
IEEE double
Double precision
In computing, double precision is a computer number format that occupies two adjacent storage locations in computer memory. A double-precision number, sometimes simply called a double, may be defined to be an integer, fixed point, or floating point .Modern computers with 32-bit storage locations...
quadruple (new in RFC1832)
enumeration
Enumerated type
In computer programming, an enumerated type is a data type consisting of a set of named values called elements, members or enumerators of the type. The enumerator names are usually identifiers that behave as constants in the language...
structure
Struct
struct is a computer science term for a record that is used to store more than one value.struct is used in the following programming languages:* struct * struct vs. C++ classes...
string
String (computer science)
In formal languages, which are used in mathematical logic and theoretical computer science, a string is a finite sequence of symbols that are chosen from a set or alphabet....
fixed length array
variable length array
union
Tagged union
In computer science, a tagged union, also called a variant, variant record, discriminated union, or disjoint union, is a data structure used to hold a value that could take on several different, but fixed types. Only one of the types can be in use at any one time, and a tag field explicitly...

– discriminated union
fixed length opaque
Opaque data type
In computer science, an opaque data type is a user defined data type used like built-in data type. It is incompletely defined in an interface, so that ordinary client programs can only manipulate data of that type by calling procedures that have access to the missing information.-Overview:Opaque...

data
variable length opaque
Opaque data type
In computer science, an opaque data type is a user defined data type used like built-in data type. It is incompletely defined in an interface, so that ordinary client programs can only manipulate data of that type by calling procedures that have access to the missing information.-Overview:Opaque...

data
void – zero byte quantity
optional – optional data is notated similarly to C pointers, but is represented as the data type "pointed to" with a boolean "present or not" flag.

External links

The XDR standard exists in three different versions in the following RFC's:

RFC 4506 2006 This document makes no technical changes to RFC 1832 and is published for the purposes of noting IANA considerations, augmenting security considerations, and distinguishing normative from informative references.
RFC 1832 1995 version. Added Quadruple precision floating point to RFC 1014.
Cisco's XDR: Technical Notes
jsxdrapi.c, the main source file of SpiderMonkey that uses XDR
xdr.cpp main xdr source file used in Firebird remote protocol
http://www.cs.rpi.edu/~hollingd/netprog/notes/xdr/xdr.pdf
The GNU Libc implementation of rpcgen, the XDR parser.
Mu Dynamics Research Labs racc grammar for XDR
IvmaiAsn ASN1/ECN/XDR Tools (a collection of tools containing an XDR/RPC-to-ASN.1 converter)

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

History

XDR data types

See also

External links