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Database Drivers

Choosing the Right Database Driver

Common Database Driver Features

Driver Strings

dBaseIV:Specifications

dBaseIV:Data Types

dBaseIV:Supported Commands and Attributes

dBaseIV:Driver Strings

dBaseIV:Other

dBaseIV:Specifications

The dBase4 file driver is compatible with dBase IV. The default data file extension is *.DBF.

Keys and Indexes exist as separate files from the data file. Keys are dynamic–they automatically update as the data file changes. Indexes are static–they do not automatically update, but instead require the BUILD statement for updating. The default file extension for the index file is *.NDX.

dBase IV supports multiple index files, whose extension is *.MDX. The miscellaneous section describes procedures for using .MDX files.

The driver stores records as fixed length. It stores memo fields in a separate file. The memo file name takes the first eight characters of the File Label plus an extension of .DBT.

dBase IV was never as widely adopted as dBase III. Choose this driver only when you must share data with an end-user using dBase IV.

dBaseIV:Data Types

The xBase file format stores all data as ASCII strings. You may either specify STRING types with declared pictures for each field, or specify native Clarion types, which the driver converts automatically.

If your application reads and writes to existing files, a pictured STRING will suffice. However, if your application creates a dBase IV file, you may require additional information for these dBase IV types:

*      To create a Numeric field in the Data Dictionary, choose the REAL data type. In the External Name field on the Attributes tab, specify 'NumericFieldName=N(Precision,DecimalPlaces)' where NumericFieldName is the name of the field, Precision is the precision of the field and DecimalPlaces is the number of decimal places. With a REAL data type, you cannot access the Character or Places fields in the Field definition, you must specify those attributes with an expression in the External Name Field on the Attributes tab.

For example, if you want to create a field called Number with nine significant digits and two decimal places, enter 'Number=N(9,2) in the External Name field on the Attributes tab of the Field properties in the Data Dictionary.

If you're hand coding a native Clarion data type, add the NAME attribute using the same syntax.

If you're hand coding a STRING with picture, STRING(@N-_9.2), NAME('Number'), where Number is the field name.

*      To create a Logical field, using the data dictionary, choose the BYTE data type. There are no special steps; however, see the miscellaneous section for tips on reading the data from the field.

If you're hand coding a STRING with picture, add the NAME attribute: STRING(1), NAME('LogFld = L').

*      To create a Date field, using the data dictionary, choose the DATE data type, rather than LONG, which you usually use for the TopSpeed or Clarion file formats.

*      MEMO field declarations require the a pointer field in the file's record structure. Declare the pointer field as a STRING(10) or a LONG. This field will be stored in the .DBF file containing the offset of the memo in the .DBT file. The MEMO declaration must have a NAME() attribute naming the pointer field. An example file declaration follows:

File FILE, DRIVER('dBase4')

Memo1 MEMO(200),NAME('Notes')

Memo2 MEMO(200),NAME('Text')

Rec   RECORD

Mem1Ptr LONG,NAME('Notes')

Mem2Ptr STRING(10),NAME('Text')

     END

    END

Use the File Import Utility in the Clarion Dictionary Editor to define your files.

dBaseIV:File Specifications/Maximums

File Size:             2,000,000,000 bytes

Records per File:      1,000,000,000

Record Size:           4,000 bytes

Field Size

 Character:           254 bytes

 Date:                8 bytes

 Logical:             1 byte

 Numeric:             20 bytes including decimal point

 Float:               20 bytes including decimal point

 Memo:                64K (see note)

Fields per Record:     512

Field Name:            12 characters

Keys/Indexes per File:

     .NDX:            No Limit

     .MDX             47 tags per .MDX files

Key Sizes

 Character:           100 bytes

 Numeric, Date:       8 bytes

Memo fields per File:  Dependent on available memory

Open Files:            Operating system dependent