World Meteorological Organizations (WMO)
Observing and Information Systems Department
WMO Information System (WIS)
Interoperability Standards at
Levels of Syntax and Semantics
Presented
by Eliot Christian <[email protected]>
at the First Meeting of
WMO / CBS / ISS / ET-ADRS
(Expert Team On Assessment Of Data Representation Systems)
in Silver Spring, MD, USA
on 23 - 25 April 2008
Syntax and Semantics
 Semantics deals with the meaning
of a symbol in some language
 Syntax deals with handling of symbols
independent of their meaning, e.g.,
 ASN.1 (Abstract Syntax Notation)
 XML (eXtensible Markup Language)
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Standards-based Interoperability
at the Level of Syntax
 Structure Types, e.g.,
 sub-element is part of element
 record is part of file
 table has three dimensions
 Data Types, e.g.,
 integers or decimal numbers ...
 dates, times, coordinates ...
 text, images, sound ...
 Indicating structure in an instance, e.g.,
 start-position, length
 mark-up with start-end tagging
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ASN.1 Snippet
PDU ::= CHOICE{
searchRequest [22] IMPLICIT SearchRequest,
searchResponse [23] IMPLICIT SearchResponse,
SearchRequest ::= SEQUENCE{
resultSetName [17] IMPLICIT InternationalString,
databaseNames [18] IMPLICIT SEQUENCE OF DatabaseName,
query
[21] Query
SearchResponse ::= SEQUENCE{
resultCount
numberOfRecordsReturned
nextResultSetPosition
searchStatus
resultSetStatus
records
[23] IMPLICIT INTEGER,
[24] IMPLICIT INTEGER,
[25] IMPLICIT INTEGER,
[22] IMPLICIT BOOLEAN,
[26] IMPLICIT INTEGER,
Records OPTIONAL,
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Comparing ASN.1 and XML
Syntactic Mechanisms
syntax description
ASN.1
XML
specification
schema
structure mechanism start-position
and length
mark-up with
start-end tags
atomic element
character
bit
encoding mechanism encoding rules
Unicode filter
(basic, packed...) (ISO 8859-1,
UTF-8 ...
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ASN.1 and Encoding Rules
In ASN.1, concrete syntax ("on-the-wire encoding")
is handled separately from the abstract syntax:
ASN.1 "Encoding Rules" are applied to make actual
messages in compliance with an ASN.1 specification
 Basic Encoding Rules (BER): represent each byte
present, as defined in the specification
 Packed Encoding Rules (PER): group repeated bytes
 Distinguished Encoding Rules (DER): represent only
bytes that change, on a message to message basis
 XML Encoding Rules (XER): translate between ASN.1
elements and their XML equivalents
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ASN.1 and XML Interoperability
using XML Encoding Rules
 An XML Encoding Rules (XER) tool can generate,
automatically and losslessly:
 an XML schema from an ASN.1 specification
OR
 an ASN.1 specification from an XML schema
 In addition, XER can be applied at the instance
level rather than the schema level, i.e.,
XER converters inserted at both ends of a
communications link will enhance transmission
efficiency "on-the-fly"
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Example: Common Alerting Protocol
Uses XER to Bridge ASN.1 and XML
 Common Alerting Protocol (CAP) standardizes
all-hazards, all-media public warning messages
 Message formats in the CAP standard were
originally defined using XML Schema
 XER was used to create an ASN.1 specification
for CAP messages, required for ITU adoption
 International Telecommunication Union (ITU)
adopted CAP as ITU Recommendation X.1303
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Standards-based
Interoperability
at the Level of
Semantics
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Standards-based Interoperability at the
Level of Semantics
 Semantic interoperability is often constrained in
practice by a lack of available data definitions
 It is risky to integrate or transform any data or
information element without its explicit definition
 ISO/IEC 11179, Metadata Registries, provides
useful guidance for documenting the meanings of
data or information elements
 The objective is to have good definitions for data
and information elements, not to fully automate
inferencing (sometimes called "Semantic Web")
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Example: CAP Data Dictionary
Element
Name
Context.
Class.
Attribute.
Representation
Definition and (Optionality)
Notes or Value Domain
alert
cap.
alert.
group
The container for all
component parts of the
alert message
(REQUIRED)
(1) Surrounds CAP alert message sub-elements.
(2) MUST include the xmlns attribute referencing the CAP URI as the namespace, e.g.:
<cap:alert xmlns:cap="urn:oasis:names:tc:emergency:cap:1.1">
[sub-elements]
</cap: alert>
(3) In addition to the specified sub-elements, MAY contain one or more <info> blocks.
identifier
cap.
alert.
identifier
The identifier of the alert
message (REQUIRED)
(1) A number or string uniquely identifying
this message, assigned by the sender
(2) MUST NOT include spaces, commas, or restricted characters (< and &)
sender
cap.
alert.
sender.
identifier
The identifier of the sender
of the alert message
(REQUIRED)
(1) Identifies the originator of this alert. Guaranteed by assigner to be unique globally;
e. g., may be based on an Internet domain name
(2) MUST NOT include spaces, commas, or restricted characters (< and &)
sent
cap.
alert.
sent.
time
The time and date of the
origination of the alert
message (REQUIRED)
The date and time is represented in [dateTime] format (e.g., "2002-05-24T16:49:0007:00" for 24 May 2002 at 16: 49 PDT).
status
cap.
alert.
status.
code
The code denoting the
appropriate handling of the
alert message
(REQUIRED)
Code Values:
“Actual" Actionable by all targeted recipients
“Exercise" Actionable only by designated exercise participants; exercise identifier
should appear in <note>
“System" For messages that support alert network internal functions.
“Test" Technical testing only, all recipients disregard
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Actions Proposed
 Syntactic interoperability should be achieved
using automated transformations, based on
standardized syntax description languages
 Syntactic interoperability cannot assure that
information is meaningful--precise definitions of
data and information elements are necessary
 ISO/IEC 11179, Metadata Registries, provides
useful guidance for defining elements, within
and among data dictionaries
 A policy promoting use of ISO/IEC 11179 would
complement broader use of ISO 191xx series of
standards, especially ISO 19115
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References:
GEOSS (Global Earth Observation System of Systems)
10 Year Implementation Plan and Reference Document
http://earthobservations.org/
ISO/IEC 11179 Metadata Registries
http://standards.iso.org/ittf/PubliclyAvailableStandards/
c035343_ISO_IEC_11179-1_2004(E).zip
Questions?
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Using Registries
to Manage
Data / Metadata
Syntax and
Semantics
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Registries are Tools for
Data Management,
Information Management,
Knowledge Management
 Several types of “registries” commonly used
 The types of registries have related content,
but extended and utilized in different ways
 The registries vary according to:
 intended purpose
 granularity of contents
 the level of semantics management
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Types of Registries
ISO 11179
Registries
Database
Catalogs
UDDI
Registries
Common Content
Common Content
Common Content
OASIS/ebXML
Registries
CASE Tool
Repositories
Common Content
Common Content
Software
Component
Registries
Common Content
Ontological
Registries
Common Content
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Example using "Country Name" as
Common Content across Registry Types
Database
Catalogs
ISO 11179
Registries
Common Content
Common Content
Common Content
OASIS/ebXML
Registries
Common Content
Software
Component
Registries
UDDI
Registries
Country
Name
CASE Tool
Repositories
Common Content
Ontological
Registries
Common Content
Common Content
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"Country Name" in a 11179 Registry
Data
Element
Concept
Name: Country Identifiers
Context:
Definition:
Unique ID: 5769
Conceptual Domain:
Maintenance Org.:
Steward:
Classification:
Registration Authority:
Others
Algeria
Belgium
China
Denmark
Egypt
France
...
Zimbabwe
Data Elements
ISO 3166
French Name
ISO 3166
2-Alpha Code
ISO 3166
3-Alpha Code
ISO 3166
3-Numeric Code
Algeria
L`Algérie
DZ
DZA
012
Belgium
Belgique
BE
BEL
056
China
Chine
CN
CHN
156
Denmark
Danemark
DK
DNK
208
Egypt
Egypte
EG
EGY
818
France
La France
FR
FRA
250
...
...
...
...
...
Zimbabwe
Zimbabwe
ZW
ZWE
716
ISO 3166
English Name
Name:
Context:
Definition:
Unique ID: 4572
Value Domain:
Maintenance Org.
Steward:
Classification:
Registration
Authority:
Others
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Registries Address Different Needs
Example using "Country Name" as Common Content
Database
Catalogs
Common Content
ISO 11179
Registries
Data
Element
Common Content
Table
Column
UDDI
Registries
Common Content
Business
Specification
OASIS/ebXML
Registries
XML Tag
Country
Name Attribute
Common Content
Software
Component
Registries
Common Content
CASE Tool
Repositories
Common Content
Term
Hierarchy
Business
Object
Ontological
Registries
Common Content
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Types of Registries:
Database Catalogs/Data Dictionaries/ Repositories
Database
Catalogs
Common Content
 Registers schema, integrity & operational information
 Includes all elements of database schemas: data elements,
relations, integrity constraints
 Emphasis on information required to make database systems
work for queries, etc., not semantic management
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Database Catalog
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Types of Registries:
Universal Description, Discovery, and Integration (UDDI) Registries
 Registers Web-based Business Services
 A White page directory of the business
activities of firms
 Emphasis on interface specifications
UDDI
Registries
Common Content
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UDDI Registry
Business-to-Business
<?xml version="1.0"?>
<shipTo>
<name>Alice Wilson</name>
<street>161 North Street</street>
<city>Happy Valley</city>
<state>MO</state>
<zip>63105</zip>
<country code>USA</country code>
</shipTo>
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Types of Registries:
Case Tool (Encyclopedias/Repositories)
 Registers data models and application
program logic
 Includes information needed to create a
database and potentially the program code
for a system, including database schemas
CASE Tool
Repositories
Common Content
 Emphasis not on semantic management
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Case Tool Repository
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Types of Registries:
Ontological Registries
 Registers Concept Structures
 Includes relations among concepts
(subsumption, inheritance,…) and
axioms for inference among concepts,
e.g., temporal/spatial reasoning, etc.
 Emphasis is on semantics
Ontological
Registries
Common Content
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Ontological Registry
Concept
Concept
Concept
Concept
Geographic Area
Geographic Sub-Area
Country
Country Identifier
Country Name
Short Name
Mailing Address
Country Name
Long Name
Distributor
Country Name
Country Code
ISO 3166
2-Character
Code
ISO 3166
3-Numeric Code
Interoperability Standards at Levels of Syntax and Semantics
ISO 3166
3- Character
Code
FIPS Code
27
Types of Registries:
Software Component Registries
 Registers reusable software components built on
specific vendor platforms such as EJB, COM,
CORBA IDL etc.
 Includes basic common elementary objects and
object patterns
 Emphasis on reusability of software component to
build flexible and standardized business systems.
Software
Component
Registries
Common Content
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An Example of Software Component Registry
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Types of Registries:
OASIS/ebXML XML Registries
 Registers XML Artifacts
OASIS/ebXML
Registries
Common Content
 Includes schemas and DTDs (XML
schemata typically relate to a paper
form, EDI document, or reporting
requirement)
 Emphasis on syntactic (structure)
information
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OASIS/ebXML
XML Registry
Repository
Dollars
X12
UnitPrice
EDIFACT
ListPrice
Currency
VI304
Collaboration
Partner #1
Schema or Template
<?xml version="1.0"?>
<shipTo >
<name>Alice Wilson</name>
<street>161 North Street</street>
<city>Happy Valley</city>
<state>MO</state>
<zip>63105</zip>
<country code>USA</country code>
</shipTo>
Collaboration
Partner #2
Schema or Template
<Rep href= “http://www.disa.mil”>DISA</Rep>
<Rep href= “http://www.disa.mil”>DISA</Rep>
<ELEMENT rep= ‘DISA’ name=‘Country’ Biz =‘VI304’ >
<ELEMENT rep= ‘DISA’ name=‘CntryCode’ Biz =‘VI304’ >
XML Instance
XML Instance
<Country>JPN</Country>
<CntryCode>JPN</CntryCode>
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Types of Registries:
ISO 11179 Metadata Registries
ISO 11179
Registries
Common Content
 Registers Data Elements, components of data
elements and groups of data elements
(e.g., country codes for customer place of
residence)
 Includes data element concepts, data elements
(including representation), value domains, and
(multiple) taxonomies
 Emphasis on semantic information such as
definitions of data elements and value
meanings, and stewardship responsibilities
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ISO 11179 Registry
Data Element List – Address Group
33c
Name
Street Address
City, State Postal Code
Country
<?xml version="1.0"?>
<shipTo >
<name>Alice Wilson</name>
<street>161 North Street</street>
<city>Happy Valley</city>
<state>MO</state>
<zip>63105</zip>
<country code>USA</country code>
</shipTo>
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