The research on Metadata Management of Resource and Environment Spatial Database
2.2 Data dictionary
The data dictionary has described the characteristic of the metadata of designed bye UML. It takes subset , substance and element as the unit , and has described the structural relation and the attribute of substance and element at this architecture . It possesses as follows the attribute : Name , short name , definition , obligation/condition , maxim occurrence , data type and domain .
The sum has formed the complete metadata according to the data dictionary with metadata’s static structure figure in UML, and has the distinct logical organization. It is easy to understanding , being easy to program to realize .
Table 1 Example of metadata for Resource and
Environment Database data dictionary
| |
Name |
Definition |
Obligation/Condition |
Maxim Occurrence |
Data type |
Domain |
| 1 |
Metadata_Identification |
Basic information required uniquely identify a resource or
resources |
M |
1 |
Aggregated
class(MD_Metadata) |
Lines 1-55 |
| 2 |
Dataset Chinese Name |
Chinese Name of Dataset |
M |
1 |
Character String |
Free Text |
| 3 |
Dataset English Name |
English Name of Dataset |
O |
1 |
Character String |
Free Text |
| 4 |
Date |
Date of publish or
update |
M |
1 |
Integer |
YYYY MM DD |
3 Metadata Management
3.1 What’s the problem?
Metadata structure as well as data dictionary clearly tell user how to describe the data base with the metadata with what UML described. All data sets can come to describe with the metadata. But how to manage the meta database , and how more effectively to help user gains the data, it need to have the good metadata management system .
The objective of metadata management is in order to procure , checks up , saves , deals with and to apply to the geographic metadata . Geographic information sharing is above the foundation of network, therefore the so-called management problem also is on the network, involving web browser, web server and metadata server, and relies on a series of requirement and the answer courses between the software parts.
At present international and internally all build many metadata systems. Such as, what it was recommendation of FGDC's is used to build the information interchange package of software of center (Clearinghouse) in space with I-Site's Freeware bundle by FGDC recommended . There has been such Web Site ( www.nsii.gov.cn ) in the National Geographic Information Exchange Center ( NGIEC ) , and user can inquire about that each node comes out well in a photograph the metadata of spatial information by way of the browser . There are other fairly more famous MetaStar's series by Blue Angel Technologies's development that has had commercialization , the Metadata DOCUMENT of ARC/INFO etc. . Analyzing these metadata management systems , can reaching them , the major merit can the module below all possessing :
The metadata browser : Being responsible for spatial data browsing and the navigation of database , and providing the query interface , as well as the data preview merit abilities
The metadata editor : Realize various editor's merit abilities of metadata , like builds and inserting and deleting and updating etc
The metadata server : Manage the metadata database , and publish metadata at the network.
Contacting the real application, and still should strictly think over following several problems when realizing the RESD to manage the system except realizing the mentioned above merit ability :
-
In each kind relation that reaches them in the metadata static figure in UML should be shone upon distinctly in the organization of metadata, and has the good query strategy .
- Owing to the fact that the project involves each domain of nature, society , economy and population , the metadata standard can not contained all aspects . Therefore being only to take some important and public metadata substances (otherwise the substance in the metadata standard can become to such an extent that numerous and jumbled ,but gives rise to in really the application a large number of superfluous surplus ) . But, as for some domains , will need to expand the metadata ( must be according to fixed rule , and by way of conformance testing ) of self , otherwise can not effectively describe the data set. So the expandability of metadata is very important .
- Using for convenient , the metadata file of standard that can export and import is various fit . The model of the storage of metadata can be adopted the method that the document system storage combines DBMS each other.
- The user interface is convenient to operating.