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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"><HTML><HEAD> <TITLE>OTL 4.0, OTL stream class</TITLE> <META NAME="Author" CONTENT="Sergei Kuchin"> <META NAME="GENERATOR" CONTENT="Mozilla/3.03Gold (Win95; I) [Netscape]"> <META NAME="KeyWords" CONTENT="OTL, Oracle, ODBC, DB2, CLI, database API, C++, Template Library"></HEAD><BODY><H1 ALIGN=CENTER>OTL 4.0, OTL stream concept</H1><H1><A NAME="otl_stream"></A>OTL stream concept</H1><P>Any SQL statement, PL/SQL block or a stored procedure call is characterizedby its input / output [variables]. </P><P><B>Example 1.</B> A SELECT statement has scalar input variables thatare used in the WHERE clause of the statement. The SELECT statement alsodefines output columns. Potentially, the output columns are vector parameterssince the SELECT statement may return multiple rows. </P><P><B>Example 2. </B>An INSERT statement writes data into a table, i.e.it has input parameters. Same is true for UPDATE statemements. </P><P><B>Example 3.</B> A DELETE statement deletes rows from a table. Deletioncriteria needs to be entered, thus the DELETE statement has input.</P><P><B>Example 4. </B>A stored procedure may have input and/or output parameters.Usually, stored procedure parameters are scalars. There is a special case,though: stored procedure returning a referenced cursor (Oracle) or a resultset (MS SQL Server or Sybase).</P><P><B>Example 5. </B>An arbitrary PL/SQL block may have input or/and outputparameters that may be either scalars or vectors.</P><P><A NAME="bulk"></A>Industrial strength database servers have bulk (orarray) operations:</P><UL><LI>bulk INSERT</LI><LI>bulk UPDATE</LI><LI>bulk DELETE</LI><LI>bulk SELECT</LI></UL><P>Therefore, parameters in INSERT/UPDATE/DELETE statement may be vectorsif the statement is performed in bulk.</P><P>The picture is clear: any interaction with SQL or its procedural extensioncan be treated as a black box with input and/or output. It does not matterwhat the black box does inside (according to the definition of a blackbox). What matters is the <I><TT>input wires</TT> </I>that send signals<I>into</I> the box and the <I>output wires</I> that receive signals <I>from</I>the box:</P><CENTER><P><IMG SRC="otlodbc.gif" HEIGHT=420 WIDTH=420></P></CENTER><P>Some of the wires may be both <I>input </I>and <I>output</I>. </P><P>Why not combine the concept of data streams and SQL? Instead of multiplyingconstructs and making database API's too convoluted, why not unify andsimplify them? The OTL gives an answer to those questions and the answeris the <A HREF="otl3_stream_class.htm">otl_stream class</A>.</P><P>Since a SQL statement may be done in bulk, the otl_stream is a bufferedstream. Conceptually, the otl_stream has two separate buffers: input andoutput. The input buffer is comprised of all input variables put together.Respectively, the output buffer is comprised of all output variables puttogether. </P><P>C++ streams are usually manipulated via operator >> and operator<<. The stream reference is on the left of the operator symbol: </P><PRE> s>>variable; s<<variable;</PRE><P>The double arrow shows the direction in which data goes: </P><UL><LI>>> -- from the stream into the data container (variable)</LI><LI><< -- from the data container (variable) into the stream</LI></UL><P>OTL streams are similar to buffered C++ streams . A SQL statement orstored procedure call is opened as an ordinary buffered stream. The logicof the OTL stream operations remains the same as the C++ stream operationswith the only exception -- the OTL stream has separate input and outputbuffers which may overlap. </P><P>The OTL stream has a flush function for flushing its input buffer whenthe buffer gets full and a collection of >> and << operatorsfor reading and writing objects of different data types. The most importantadvantage of the OTL streams is their unified interface to SQL statementsand stored procedure call of any kind. This means that the applicationdeveloper needs to remember just a few syntactical constructs and functionnames which he already got familiar with when he started working with C++streams. </P><P>Inside the OTL stream there is a small parser for parsing <A HREF="otl3_bind_variables.htm">declarationsof bind variables and their data types</A>. There is no need to declareC/C++ host variables and bind them with placeholders by special bind functioncalls. All necessary buffers are created dynamically inside the stream.The stream just needs to be opened for reading and writing values.</P><P>The OTL stream interface requires use of the OTL exceptions. This meansthat potentially any OTL stream operation can throw an exception of the<A HREF="otl3_exception_class.htm">otl_exception</A> type. In order tointercept the exception and prevent the program from aborting, wrap upthe OTL stream code with the corresponding try & catch block.</P><P>The functioning of the otl_stream is pretty much automatic: when allof the input variables of the stream are defined (in other words, the inputbuffer is filled out), it triggers the block box inside the stream to execute.The output buffer gets filled out in the process of the execution of theblack box. After the execution is finished, the output values can be readfrom the stream. If it is a SELECT statement and it returns more rows thanthe output buffer can hold, after the whole output buffer is read, thenthe stream automatically fetches the next bacth of rows into the outputbuffer.</P><P><HR WIDTH="100%"></P><CENTER><P><A HREF="otl3_intro.htm">Prev</A> <A HREF="otl3_class.htm">Next</A><A HREF="otl3.htm">Contents</A> <A HREF="home.htm">Go Home</A> </P></CENTER><P>Copyright © 1996, 2008, Sergei Kuchin, email: <A HREF="mailto:skuchin@aceweb.com">skuchin@aceweb.com</A>,<A HREF="mailto:skuchin@gmail.com">skuchin@yahogmail</A><SCRIPT Language="JavaScript"><!-- hide from old browsers var modDate = new Date(document.lastModified) document.write("<i> Last Updated:</i> " + (modDate.getMonth()+1) + "/" + modDate.getDate() + "/" + "0"+(modDate.getYear())%100+"."); //--> </SCRIPT>.</P><P><I>Permission to use, copy, modify and redistribute this document forany purpose is hereby granted without fee, provided that the above copyrightnotice appear in all copies. </I></P><script type="text/javascript">var gaJsHost = (("https:" == document.location.protocol) ? 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