Application Development in Visual Basic CP3013

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Application Development in Visual Basic - CP3013

• Data Access Technologies

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• Embedded SQL cf Call Level Interface

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Embedded SQL Interface (1)

• Not provided with ODBC
• Method combining
• computing power of high-level language like C/C
  and
• database manipulation capabilities of SQL.
• coded in application programs source code
• Allows you to execute any SQL statement from an
  application program.

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Embedded SQL Interface (2)

• A program containing embedded SQL can be compiled
  in two steps.
• Precompiler recognizes SQL statements embedded in
  program,
• Replaces them with native calls to functions in
  SQL/db runtime library.
• Output pure C/C code with pure C/C portions
  intact.
• Regular C/C compiler used to compile code and
  produce executable.

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Call Level Interface (1)

• Available in ODBC
• Call Level Interface (CLI) is callable SQL
  interface to database servers
• MS ODBC and International Standard specifications
  for SQL/CLI,
• Special db API
• for relational database access
• gives functions so application can send SQL code
  to db at runtime

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Call Level Interface (2)

• Has Functions
• For client applications to call
• Which pass dynamic SQL (may cover later)
  statements as function arguments
• Alternative to embedded dynamic SQL
• Unlike embedded SQL, does not require host
  variables or precompiler.
• SQL code in client application
• not pre-compiled
• interpreted at run-time

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Differences between CLI and Embedded SQL (1)

• Application using embedded SQL interface requires
  
• precompiler to convert the SQL statements into
  code,
• which is then compiled, bound to the database,
  and executed.
• A CLI application
• does not have to be precompiled or bound
• instead uses standard set of functions to execute
  SQL statements and related services at run time.

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Differences between CLI and Embedded SQL (2)

• Difference important because,
• traditionally, precompilers have been specific to
  each db product,
• effectively ties applications to that product.
• CLI enables you to
• write portable applications independent of any
  particular db product.
• independence means CLI applications do not have
  to be recompiled or rebound to access different
  db.
• just connect to appropriate db at run time.