Design and Implementation of Iran’s National Spatial Data Clearinghouse Network

Geomatic2012, NCC, Tehran

Abstract

Iranian National Cartographic Center (NCC) is in charge of developing SDI in

Iran, according to the 5th national development plan of the country. In this

respect, NCC has started design and development of national spatial data

clearinghouse network. The architecture of this network is based on the second

generation of clearinghouse networks (10). Development of National Geoportal

as well as motivating individual ministries and national organizations to develop

their own catalogue ue services and metadata repositories as part of this

network, are different activities relevant to the development of national spatial

data clearinghouse network. This network is being developed based on national

standards to facilitate the connection of that with the networks of other countries

at the regional/global levels. This paper aims to describe the architecture of the

clearinghouse network and activities for the development of that.

Keywords:

Spatial Data Infrastructure (SDI), National Clearinghouse, Iranian

National Cartographic Center (NCC)

1– Introduction

According to clause 55 and Article (e) of the clause 46 of the Fifth National

Development Plan, NCC is responsible for coordinating of SDI implementation at

different levels. SDI facilitates and coordinates spatial data production, gathering,

storage, sharing, access, and optimal use in different levels, from national to

local. SDI consists of five main components including spatial data, organizations

and people, policies, standards and access networks. These components are

relating to each other and their proper development, as well as establishing

appropriate relation between them is resulted in development of SDI in the

community.

Access networks are a set of technologies and infrastructures to enable the

discovery and access the spatial data. For example, media communications,

networks and exchange environments, sharing tools and overall, technologies

related to communications are considered in this component. The best example

of access network in national-level is the national clearinghouse network.

Different interpretations of the various viewpoints have been proposed by

researchers for the clearinghouse. For example, from the viewpoint of the user,

clearinghouse is a service to obtain the information such as which organization

has what information (1). But generally, the national clearinghouse is a portal of

central web at the national level that focuses on the facilitation of discovery,

access and desirable service. In fact, national clearinghouse is a concept beyond

the data repository and provides a center for access and use of all available

spatial data across the country.

Clearinghouse itself consists of a set of components and connections between

them. These connections will be a set of services and protocols. Once,

clearinghouse has been purely provided the ability to search in metadata base

and then, this capability has gradually improved to the representation and

analysis over time. Thus, the abilities and consequently the components of

clearinghouse have evolved according to tasks, expectations and applications

with progress in the technologies and web services over time.

In order to achieve an effective clearinghouse as access network of spatial data

infrastructure, it is essential to be provided a strong link between clearinghouse

and other SDI components including people, data, policies and standards (2).

Only when a strong coherence is created between mentioned components,

clearinghouse will succeed as a component of the spatial data infrastructure.

NCC as trustee and coordinator of the SDI development in country, has designed

the national clearinghouse network in order to establish the integration and

coordination between the executive agencies for development of the national

clearinghouse network. This paper is providing the key points of the Iranian

national clearinghouse network design and describing the architecture,

components, and standards used to create a national clearinghouse network as a

collaborative and interactive network.

Then, the paper describes the concepts needed in the clearinghouse network in

the second section. In this section, at first, the clearinghouse network is

introduced and then, its various generations are explained. The third section is

devoted to the details of Iran’s national clearinghouse network. In this section, the

architecture of Iran’s national clearinghouse network and also syntactic and

semantic standards employed for interaction development has been described.

Then, the conclusion is coming.

Concepts

Clearinghouse network

National SDI facilitates and coordinates spatial data production, gathering,

storage, sharing, access, and optimal use in different levels, from national to

local. SDI consists of five main components including spatial data, organizations

and people, policies, standards and access networks. These components are

relating to each other and their proper development, as well as establishing

appropriate relation between them is resulted in development of SDI in the

community.

Access networks are a set of technologies and infrastructures to enable the

discovery and access the spatial data. For example, media communications,

networks and exchange environments, sharing tools and overall, technologies

related to communications are considered in this component. The best example

of access network in national-level is the national clearinghouse network.

A clearinghouse is based on a distributed network of people including the spatial

data producers and users that are connected electronically with each other (3).

The distributed system refers to a distributed set of users, data, software and

hardware whose aim is to achieve some predetermined targets (4). The

clearinghouse network enables the users to obtain the information about the

spatial data availability, data requirements and how to access to it. Also, the user

can realize who has the spatial data, which spatial data does it have and how is

the quality and type of data (5).

The most important reason for creating a clearinghouse is the users’ interest in

having a single source to access all existing and available resources.

Clearinghouse is a system to provide such capability as a central part for data

sharing between producers and users of data (6), (7) and (8).

There are many differences in development and implementation of the

clearinghouse network. The method used to set up a clearinghouse depends on

the technological, legal, organizational, cultural, commercial and managerial

contexts. These contexts determine the success rate of the clearinghouse.

Different names for this national facility have been proposed in the spatial

communities. For example, the Open GIS Consortium (OGC) applies the

Catalogue Service; Australia uses Spatial Data Directory; and the United States

of America applies Clearinghouse for it (9). Despite using the different names,

their common aim will be allowing for the finding and usage of the spatial data

through metadata.

The user can search the clearinghouse for spatial data with different

mechanisms. For example, the user can either use the predefined cases or

search based on the location, key words or even based on the time of the data

provision. The most popular mechanisms used by the users are the predefined

cases and key words.

Generations of clearinghouse

Clearinghouse network consists of a set of components and connections

between them that has changed with technological advances and thus the

different generations of clearinghouse network have been formed (10). In other

words, with the passing of time and technology progress, the various structures

have been designed for the clearinghouse. In a general classification, these

various structures can be expressed in three generations (10). In the following,

the explanations about these three generations will be provided.

The first generation of the spatial data clearinghouse

The first generation of the spatial data clearinghouse was created in the United

States, Australia, Netherlands, England and Canada. These clearinghouses were

similar to the existing web-based databases. In order to search a spatial data

layer, the user was asked to set the search parameters such as the geographic

range, data theme and the name of the data layer in the clearinghouse user

interface. Then, the user was provided with the requested spatial data from the

database in accordance with the search criteria. In other words, the users were

supplied with the detailed descriptions of the data -which is called metadata- and

information about how to access them or connect to the website where the data

is available in.

The second generation of the spatial data clearinghouse

As the web-based technology and the spatial web services developed, a new

generation of clearinghouse was created on the basis of the geoportals, the

catalogue services and the spatial services. This generation provided the users

with the more appropriate methods to search and access the standardized spatial

data. The popular clearinghouses in the world belong to the second generation.

The third generation of the spatial data clearinghouse and its 

architecture

The third generation of clearinghouse is called expert clearinghouse. The expert

spatial data clearinghouse is a kind of clearinghouse that not only searches the

required data directly, but will search the data that can be converted into the

required data.

Since the popular generation of the clearinghouse systems i.e. the second

generation cannot provide the appropriate data for different users with different

needs, other architecture has been proposed (10). In this architecture, the

situations have been emphasized in which the data needed by inexperienced

users does not exist with a name that the search is done base on or even

sometimes the professional users are not satisfied with search results.

Iran’s national clearinghouse network

Architecture of Iran’s national clearinghouse network

After evaluation of the different generations, architecture of Iran’s national

clearinghouse network was selected in accordance with the second-generation

network architecture.

Figure 1, illustrates the schematic structure of the second generation

clearinghouse selected for Iran’s national clearinghouse that is on the basis of

one geoportal, catalogue services and spatial services.

Figure 1: Schematic structure of the second generation clearinghouses (10)

The main elements of the second generation clearinghouse can be summarized

as follows:

• Geoportal provides the entry point to spatial information on the web. Geoportal

of a website is on the Internet in which the spatial content including the spatial

data and spatial services are found.

• Catalogue Services enable the metadata distribution on the spatial data

resources and searching metadata and querying it.

• Metadata Repository stores the information about the spatial data (in database).

• Spatial Services which are connected to the data server provide the various

services such as spatial data representation and loading for the user.

• Registry Service is where the spatial services and catalogue services are

recorded to be found by a geoportal.

In order to search for the data (or service) in a clearinghouse, users are

connected to geoportal and determine the search parameters. Then, the

geoportal searches the metadata repositories through the catalogue services for

data needed by user. Each catalogue service enables the metadata distribution

coming from each data trustee. If the server of the relevant data supports the

spatial services such as representation or loading, the user is able to see the

data or load it.

Standards of Iran’s national clearinghouse network

Syntactic standards

Syntactic standards refer to the standards required for resolving the syntactic

heterogeneity. Some important standards that are minimum requirements for

resolving syntactic heterogeneity in Iran’s national clearinghouse network were

evaluated and some of them were selected and customized in some cases

according to the national conditions and needs.

Relating to the metadata standards, ISO19115 was selected as a basis for

national metadata standard and prepared and documented by NCC. Metadata

should be provided for the spatial datasets and it can be also arbitrarily provided

for integration of datasets, features and attributes. This international standard

determines the metadata needed to describe the digital spatial data. The

metadata can be used for independent datasets, integrating datasets, specific

spatial features and numerous classes of objects comprising a feature.

In order to store and exchange the information, GML as well as, CSW, WMS,

WFS, WPS and WCS relating to OGC were selected for Iran’s national

clearinghouse network. Since the technical details of these standards are

extensive, the standards have been introduced here briefly and references will be

given to obtain more detailed information.

CSW standard designates the interfaces between clients and catalogue services

through demonstration of abstract and implement-specific models. This OGC

standard can be used for implementation of interfaces in the catalogues relating

to the various forms of information sources. The more detailed information about

this standard and its functions is available in the reference 11.

WMS is a service that prepares the maps from the spatial reference data

dynamically. Any map in WMS is displayed as an image of spatial information

such as a digital image file on the computer screen. WMS does not provide the

real spatial information as a response to a request, but maps are displayed as

raster images for this kind of information. The more detailed information about

this standard is available in the reference 12.

WFS is a standard that has been created by OGC for sending and receiving the

spatial data via HTTP. WFS is used for encoding and transmitting the information

in the form of GML which is a subset of XML. The fundamental difference

between the WFS and WMS is in terms of the sending and receiving the spatial

information. The more detailed information about this standard is available in the

reference 13.

WCS service supports the electronic retrieval of the spatial data as “coverage”

that refers to the digital spatial data representing the variable phenomena in time

and place. In fact, the WCS provides an interface to describe how to request

raster source of a spatial image. The more detailed information about this

standard is available in the reference 14.

The overall goal of WPS is access to processes having the capability of the

spatial data processing. Capabilities in preparation of the web-based maps have

gradually improved from representing data (WMS), to access the stored data and

manipulate it remotely (WFS) and finally to data processing (WPS). The more

detailed information about this standard is available in the reference 15.

GML has been designed based on structure of XML and with regard to the

requirements of ISO19118 in order to store and exchange the information. XML is

a public format for documents and data available on the web with the standard

W3C1998. This format is used for storage and exchange of data and information.

The more detailed information about this standard is available in the reference

16.

Semantic standards

The semantic standards are standards needed to resolve the semantic

heterogeneity. Standards intended to resolve the semantic heterogeneity

includes three popular standards: OWL, OWL-S and WMSL.

OWL is an ontology language designed for the semantic web that will present a

rich set of operators to form the descriptions of the concepts. This language is a

W3C standard that accelerates the interaction and sharing between functions

and has been designed in such a way that is consistent with the existing web

standards (17).

When it is need to process the information within a document by an application in

addition to represent the contents to the user, OWL is used. The OWL can be

used to provide the meaning of words and the relationships between them

explicitly. This provision of the words and relationships between them is called

ontology. OWL has more facilities for expressing the meaning and semantic

comparing with XML, RDF, and RDF-S, and thus the ability of OWL is more than

these languages to provide the contents interpretable for the machine on the

web. OWL is a revision of DAML+OIL web ontology language that combines the

experiences coming from the designing and applying DAML+OIL (18).

For applying a web service, agent software requires an interpretable description

of that service by machine and a tool available by it. So, an important goal for the

mark languages in the semantic web is making a framework in which these

descriptions are produced and shared. Websites should be able to employ a set

of the base classes and characteristics for declaring and describing the services.

The mechanisms in structure of OWL ontology provide an appropriate framework

for achieving this. Such language is called OWL-S. It is expected that The OWLS

takes the following types of actions:

• Finding the web service automatically

• Requesting from the web service automatically

• Automated integration and interaction of the web service

• monitoring the automated implementation of web service

The Web Service Modeling Language (WSML) provides a language framework

for semantic Web services based on the conceptual model of the Web Service

Modeling Ontology (WSMO) (19). WSML is providing a tool for semantic web

service description and related aspects, namely the ontology, web services,

goals, and mediators. The purpose of these descriptions is to automate the tasks

related to web services, such as finding, mediation and request. The arguments

based on the formal descriptions can be used to achieve automation. The

modeling, ontology and the logical expressions are addressed in this section.

The different applied scenarios require the different expressivenesses of the

logical formalisms. For example, in the context of requesting web services, it has

proven that the different levels of the formalism are required depending on the

concrete scenarios. However, interaction and reuse of the ontology of the shared

domain is essential in those different layers. WSML provides such a framework

that includes the appropriate stratification and enables applying the shared

terminologies.

Conclusion

Since NCC has been selected to be responsible for coordinating of SDI

implementation at different levels, according to clause 55 and Article (e) of the

clause 46 of the Fifth National Development Plan, it has designed the national

clearinghouse network in order to establish the integration and coordination

between the executive agencies for development of the national clearinghouse

network as trustee and coordinator of the SDI development in country.

According to various studies conducted in the field of clearinghouse in different

countries, the architecture of second generation of clearinghouse was determined

as the basis of architecture of Iran’s national clearinghouse. The main

components of the national clearinghouse are based on the architecture of the

second generation including geoportal, catalogue services, metadata repository,

spatial services and registry service whose duties and their relationships have

been determined. Considering the distributed structure of this generation of

clearinghouse networks, it is necessary to comply with the certain standards –

which have been determined as syntactic and semantic standards for Iran’s

national clearinghouse- to achieve interoperability between the various

components.

REFERENCES

1. Rajabifard, A, Feeney, M.E and Williamson, I.P., Future directions for SDI

development. s.l.: International Journal of Applied Earth Observation and

Geoinformation, 2002b, Vol. 4. 11-12.

2. Rajabifard, A and Williamson, I.P., (2001), Spatial Data Infrastructures: an

initiative to facilitate spatial data sharing. In Global Environmental Databases

Present Situation and Future Directions. [book auth.] R. Tateeishi and D.

Hastings. Hastings (Hong Kong): International society for photogrammetry and

remote sensing, Vol. 2.

3. Clinton, W., (1994), Coordinating Geographic Data Acquisition and Access to

the National Spatial Data Infrastructure. Washington DC: Executive order 12096,

Federal Register, Vol.59,17671-4.

4. Bishr, Y. and Radvan, M. (2002), worldwide developments of national spatial

data clearinghouses 687 concepts, cases and good practice, [book auth.] R

Groot and J. McLaughin. Geospatial Data Infrastructure. s.l.: Oxford: Oxford

University Press.

5. Radwan, M., (2002), the development of Geographic Information Infrastructure

‘GDI/SDI’ to support access to spatial data in distributed environment.

6. Philips, A., (1998), A metadata management system forvweb-based SDIs. MSc

thesis. s.l.: Department of Geomatics, university of Melborne.

7. Noori-Bushehri, S and Rajabifard, A., (2001), A proposal for a workshop on

APSDI clearinnghouse. Tsukuba, Japan: 7th PCGIAP meeting.

8. Rajabifard, A., (2002), Diffusion for regional spatial data infrastructures:

particular reference to Asia and the Pacific. PHD thesis. s.l.: University of

Melborne.

9. Crompvoets, J; Bregt, A; Rajabifard, A; Wiliamson, I., (2004), assesing the

worldwide developments of national spatial data clearinghouse. 7, s.l.: J

Geographical Information Science, Vol.18, 665-689.

10. Mansourian, A; Omidi, E; Toomanian, A; Harrie, L., (2001), Expert system to

enhance the functionality of clearinghouse services. s.l.: elsevier, Vol. 35.