Abstract Syntax Notation One (ASN.1) is a standard for describing structured data.
Combined with a standard for encoding this data, such as
BasicEncodingRules (BER), DistinguishedEncodingRules (DER), CanonicalEncodingRules (CER), or PackingEncodingRules (PER), it can serve as one of the AlternativesToXml.

Overview of ASN.1:
http://www.oss.com/asn1/overview.html

Summary with examples of ASN.1 and BER:
http://support.microsoft.com/kb/252648/en-us

ASN.1 with BER is used as the basis for SimpleNetworkManagementProtocol (SNMP) and MessageHandlingServices (MHS), for example.

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A variety of data encoding standards for transmission of data defined by an ASN.1 structure:

	'''BER''':	(BasicEncodingRules) ''"was created in the early 1980s and is used in a wide range of applications, such as Simple Network Management Protocol (SNMP) for management of the Internet; Message Handling Services (MHS) for exchange of electronic mail and TSAPI for control of telephone/computer interactions."''

	'''DER''':	(DistinguishedEncodingRules) specialized high-security form of BER

	'''CER''':	(CanonicalEncodingRules) large encrypted messages (and incremental parsing -- like SAX, for XML)

	'''PER''':	(PackingEncodingRules) ''"faster and more compact encodings than BER. PER is used in applications that are bandwidth or CPU starved, such as air traffic control and audiovisual telecommunications."''

	'''XER''':	(XML Encoding Rules) ASN.1 in XML.

	'''E-XER''':	''"(Extended XML Encoding Rules) [...] ASN.1 an XML schema notation as powerful as XSD, with the simplicity of ASN.1."''