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Dataset Properties - Table Join
Contents : Table Join
One of the most important issues in GIS is matching data from diverse sources together. One of the techniques to do so is Table Joining. Based on the attributes in you dataset, you can link an external data table to your dataset and embed it.
Table Joining is based on the principle of having common attribute fields. When a Spatial Object in your dataset has a value for that attribute field that is matched with the external table, the external table's row is included in the Spatial Object.
By defining a Table Join, your Spatial Objects are extended with all rows from the external table that have equal values for the defined attributes.
Table Joins are definitions. You specify the definition in this window. The joined table will become an new Attribute Set in your model and will be have as any other Attribute Set.
How to create a Join in 6 steps
1. Choose a Model.
If there are Joins defined, they will be listed in the drop-down list. You may choose on to alter it's definition.
2. Click 'New'.
Table Join Definition fields will become editable.
3. Select an external table or a database table
There are 3 ways to select a table :
- Type in a table reference (either filename or database reference)
- Open a File in a File Selection box using the Open Table… button.
- Open a Database Table using the Open Database… button. Select a Database, then a table from that database. Database connections are defined using the Data Source Administrator.
Choose a table from the file system (file formats *.txt and *.dbf are supported) :
Or choose a table from a database :
The connection parameter specifies to which database Orbit GIS must connect. Therefore, the connection needs to be known beforehand. You can define a database connection using the Database Connection tool from the Tools menu. Once the connection is made, you can enter a TABLE name, a VIEW or QUERY name.
4. Enter an Attribute Table Name .
This name will be the name of your Attribute Set and the name of your Table Join Definition. This value is obligatory.
5. Define Join
Now define the attribute match on which the join must be realized. Select the Attribute from your dataset (current Model), then select the according Attribute form the external Table. Click 'Add'. The join definition will appear in the list.
Note: Some Table Join Definitions are based upon 2 or more attributes. Repeat step 5 to enter all required attributes. You may select an attribute match in the list and remove it.
6. Execute
When your definition is complete, click 'Join Attribute Table' to instantly create a new Attribute Set from the external table, and add all matching rows to all Spatial Objects of your model.
When you now select an object from this dataset, the Object Inspector will show the joined table rows. Note that in this example, the primary field is set to a joined field, displaying the streetname (attribute 'los') instead of a list number.
When displaying the attribute table to which the join was defined, the joined attribute fields are highlighted in light yellow background. This
Storage
The Table Join Definition is saved in the Orbit Resource Descriptor file. The external table is not copied into your dataset, only the reference to it is stored. Next time you open the dataset, the Table Join will be executed again in real time. You thus have always refreshed access to the external table, but have to take care that the file or database remains available.
Once the join is completed, Orbit does not check changes to the original table file. Also, Orbit does not allow editing a Joined Table in this version. Editing of external data is expected to be done by external tools.
You may wish to export the dataset as OVF file : this will embed the external table as common attributes to the data and will loose reference to the original file.