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 Overview of the DBPX RDD
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     The DBPX driver lets you create and maintain (.db), (.px), (.x??), and
     (.y??) files with features different from those supplied with the
     original DBFNTX driver and compatible with files created under Paradox
     3.5. The new features are supplied in the form of several syntactical
     additions to database and indexing commands and functions.  Specifically
     you can:

     .  Create tables that recognize the standard CA-Clipper data
        types as well as Currency ($) and Short (S) numbers between -32,767
        to +32,767

     .  Create equally efficient keyed and unkeyed tables

     .  Create, select, and activate secondary indexes on Paradox
        tables

     The DBPX driver provides simple, seamless access to the Paradox database
     system.  The CA-Clipper application programmer who intends to access
     Paradox tables with the "VIA" clause need only include the RDD header
     file at compile time and make the appropriate libraries available at
     link time.

     Paradox stores data in tables (known to Xbase developers as data files
     (.db)'s), consisting of fields and records.  Unlike Xbase databases, a
     Paradox database refers to a group of files that are related to each
     other in some way, rather than to one file.

     Also, Paradox employs the concept of companion files, known as objects,
     that are related to the table.  Some examples of object files are report
     forms, indexes, and data entry forms.  A table and its accompanying
     objects are referred to as a family.

     It is easy to identify objects belonging to a particular family since
     they all have the same base filename and are distinguished by their
     extensions as shown in the table below.

     Paradox File Descriptions
     ------------------------------------------------------------------------
     Extension      Object
     ------------------------------------------------------------------------
     .DB            Table
     .PX            Primary Index
     .X?? or Y??    Secondary Index
     .F or F??      Data Entry Forms
     .R or R??      Report Formats
     .G or G??      Graph Specifications
     .SET           Image Settings
     .VAL           Field Validity Specifications
     ------------------------------------------------------------------------

     The DBPX driver only deals with the table and index files (.db, .px,
     .x?? and y??) so only these files are discussed here.

     Though Paradox tables are limited to 8 character filenames, each table
     can contain an unlimited number of records in files up to 256M in size.
     Paradox records in nonkeyed tables can be up to 4000 bytes each while
     keyed tables have a 1350 byte limitation.  Each record can contain up to
     255 fields of up to 255 characters each.

     There are some field naming restrictions you must observe.  Field names
     may:

     .  Although the Paradox file structure allows fields to be up to
        25 characters long, since CA-Clipper symbols can only be 10
        characters, DBPX truncates the field name to 10 characters.

     .  The Paradox file structure allows embedded spaces in field
        names.  Since this is illegal in CA-Clipper, the DBPX driver converts
        spaces into underscores (_).

     .  Not be duplicated in the same table.

     Also, most Paradox data types directly match data types in standard
     Xbase data files, with these differences:

     .  Paradox tables support both the Numeric (N) data type as well
        as a more specific Currency ($) data type.  Both the N and $ data
        types can have 15 significant digits.  Numeric types that exceed this
        length are rounded and stored as scientific notation.  Also, DBPX
        supports the Short (S) data type to represent numbers between -32,767
        and +32,767.

     .  The Alphanumeric field type allows all ASCII characters except
        embedded nulls (ASCII 0).  The Alphanumeric type is identical to the
        Character (C) data type in Xbase.  Paradox limits this field type to
        255 characters.

     .  Paradox also supports a Date (D) field type, stored as a long
        integer.  It can contain any value between January 1, 100 A.D. and
        December 31, 9999.