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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B6b. Beijing 2008 
these components are: people, access network, policy, standards 
and data. 
Technology 
Figurei. SDI components (Rajabifard & Williamson 2001 p.5) 
order to reduce expenses in the field of data collection, the data 
that is acquired by one organization should be useable for others. 
Descriptions about data quality should assure the user that the 
data are suitable for his/her purposes. There are some known 
criterions for stating quality of data. These elements are: lineage, 
positional accuracy, attributes accuracy, logical consistency and 
completeness. 
Reasons of applicability forced Salge add another elements to 
describe data quality, semantic accuracy.Semantic accuracy 
describes the number of features, relationship, or attributes that 
have been correctly encoded in accordance with a set of feature 
representation rules. Related to the meaning of the “things” of 
the universe of discourse (the reality), semantic accuracy refers 
to the pertinence of the meaning of the geographical object 
rather than to the geometrical representation [5]. 
Each dataset that is collected or updated should be evaluated in 
the context of known quality parameters like integrity, 
completeness and accuracy. It is obvious that a perfect quality 
management is needed but this paper has been limited to define 
and impose some of data quality parameters in data acquisition 
process. The following cases are the issues that this article has 
considered: 
Each of the five components is described briefly below [4]: 
The data component comprises the core data elements for the 
SDI. For example a state SDI could define geodetic control, 
cadastral information, administrative boundaries, elevation and 
hydrology data themes as fundamental. 
The avenue by which data within an SDI is made available to 
the community can be described as the access network. Access 
arrangements must be made in accordance with the policy 
decisions and technical specifications defined within the 
implementing organization’s institutional framework. 
The institutional framework of the organization implementing 
the SDI defines the policy and administrative arrangements for 
collecting, maintaining, accessing and applying the standards 
and data sets. 
1- Each object should have the right geometry type 
2- All attributes about a feature and their relations 
must be considered 
3- Values of attributes should have pertinence with 
defined attributes types 
4- Integrity constraints should be taking into 
account (for example intersection of a ditch and a 
road is forbidden) 
2.4 Web Feature Services 
For controlling the first three challenges we used the data 
schemas that are available via the appropriate Web Feature 
Services (WFS). A web feature service enables the user to 
access integrated data that are stored in a server. Using WFS we 
can have operations such as: 
The standards component defines the technical characteristics 
of the fundamental data sets. These can include metadata, data 
dictionaries, data quality, data transfer, reference systems and 
data models. 
The people component of an SDI encompasses the diversity of 
the users and producers of spatial data (including value-adding 
agents). 
These components can be classified in two groups. One of them 
consists data and people and other contains technical 
components and both of them have dynamic nature. The users 
need for different types of data and this need change with the 
time and at the other side technology developments change the 
technical components of SDI and so it can be said that the 
concept of SDI has a dynamic and changing nature. 
2.3 Data Quality 
When the producer and user of data are not the same, stating the 
data quality will be needed and producer must describe the 
quality of acquired data and in the other side the user should 
describe requirement quality for his/her work. The issue of data 
quality becomes more important when we want to share data. In 
Querying on a database and retrieving features 
Finding the definition of any object and its whole 
attributes 
Adding new feature to database 
Deleting an object from database 
Updating an object in a database 
Lock features to prevent modification 
The Web Feature Service (WFS) is easily one of the most 
valuable specifications of the OGC (one of the leaders in the 
field of standardization for SDI). It provides a generic way to 
access raw geographic data over the web. To the general user, 
this can be a wealth of information embedded in the map being 
viewed. Parts of the WMS (Web Mapping Services) tried to 
implement this functionality, but using WFS gives much more 
control over how to actually access that data [6]. 
Figure 2 shows the components necessary to serve geographic 
features and process transaction requests from client 
applications using HTTP.