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| The ACCESS Procedure for PC Files |
SAS/ACCESS Descriptors for PC Files
| Overview |
SAS/ACCESS descriptor files are the tools that the ACCESS procedure uses to establish a connection to a PC file. To create descriptor files, use the ACCESS procedure.
See: The ACCESS Procedure for PC Files. There are two types of descriptor files: access descriptors and view descriptors.
| Access Descriptors |
An access descriptor holds essential information about the structure of the PC file that you want to access. For example, you can access the file's format and name, its database field or column names, and its data types. Access descriptors can also contain the corresponding SAS information such as the SAS variable names and formats. Typically, you have only one access descriptor for each PC file.
An access descriptor describes only a PC file format and contents to SAS, that is, it is a master description file of the PC file for SAS. You cannot use an access descriptor in a SAS program. Instead, you use an access descriptor to create other SAS files, called view descriptors, that you use in SAS programs.
| View Descriptors |
A view descriptor defines some or all of the data that is described by one access descriptor (and, therefore, one PC file). For example, you might want to use only three of nine possible database columns and only some of the rows in a PC file. The view descriptor enables you to do this by selecting the database fields or columns that you want to use and specifying criteria to retrieve only the rows you want. Typically, you create several view descriptors based on one access descriptor, where each view descriptor selects a different subset of the PC files data.
A view descriptor is a SAS data set or, more specifically, a SAS data view. You use a view descriptor in a SAS program much as you would any SAS data set. For example, you can specify a view descriptor in the DATA= statement of a SAS procedure or the SET statement of a DATA step. You can use a view descriptor in a SELECT statement of the SQL procedure to join view descriptor data with SAS data, for example.
You can use a view descriptor to update data directly in some of the PC file formats, such as the DBF file format.
In some cases, you might also want to create a SAS data file from data stored in a PC file. Using a view descriptor to copy PC files data into a SAS data file is called extracting the data.
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