Autodesk 15606-011408-9330 User Guide - Page 98

Linking Attribute Data to Spatial Data Files To link the attribute data to spatial data, you simply specify the OLE DB or Autodesk DWG database table you want to use when setting up the layer. Autodesk MapGuide Author matches the records in the table to the spatial features in the SDF from which the layer was created by means of a key. A key is a string that uniquely identifies each spatial feature in the SDF and each record in the database. When a record in the attribute database and a spatial feature in the SDF have the same key, the record is linked to the spatial feature. You can also use a database table for theme information. For example, you might have three sources of data: an SDF of coordinates that represent lakes, a secondary database table containing the name and linked URL for each lake, and another database table containing theme information, such as the size of each lake, water purity, and more. When you create the layer in the Map Layer Properties dialog box in Autodesk MapGuide Author, you specify the secondary table on the Data Sources tab, and specify the theme table from the Styles tab when adding a theme. Note that neither of the tables need to contain coordinates-they are linked to the polygons in the SDF only by their keys. For more information, see "Setting Display Styles for DWG Layers" on page 171. Help Index To avoid potential conversion problems, be careful when creating the key troubleshooting field. Depending on the type of database, you might not be able to use the problems creating themes attribute data unless the key field in the database is exactly the same size as the key field in the SDF to which you are linking it. Some databases, when queried, will append the keys with blank space characters to make them the  exact length you specified for the field, so the database keys will not match those in the SDF. For more information, choose Help Contents, click the Index tab, and look up "troubleshooting, problems creating themes." Linking Attribute Data to Another Database You can create point layers and text layers from OLE DB or Autodesk DWG data sources instead of SDFs. For these layers, you can still use a OLE DB or Autodesk DWG database table for creating themes. For example, if you are setting up a layer of cities, you might have two tables: one that contains basic information about each city, such as the key, coordinates, name, and a URL link, and a second table that contains data on which you want to create themes, such as the population, majority political party, and so on. The second table would also contain the same key values as the first table; Autodesk MapGuide uses these keys to assign the theme values in the second table to the corresponding cities in the first table. 98 | Chapter 5 Working with Data in Autodesk MapGuide