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<meta name="DC.Title" content="Introduction to i5/OS DDM" />
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<title>Introduction to i5/OS DDM</title>
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<body id="rbae5intrdf"><a name="rbae5intrdf"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Introduction to <span class="keyword">i5/OS</span> DDM</h1>
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<div><p>This topic describes the purpose of distributed data management
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(DDM), the functions that DDM supplies on the <span class="keyword">iSeries™ server</span>,
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and the concepts of <span class="keyword">i5/OS™</span> DDM.</p>
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<p> DDM is part of the <span class="keyword">i5/OS</span> licensed
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program. <span class="keyword">i5/OS</span> DDM as a
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source supports Level 2.0 and below of the DDM architecture. <span class="keyword">i5/OS</span> DDM
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as a target supports Level 2.0 and below for <dfn class="term">record file</dfn> (a file
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on disk in which the data is read and written in records) types and Level
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3.0 and below of the DDM architecture for stream files (documents) and directories
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(folders).</p>
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<p>The DDM support on the <span class="keyword">iSeries server</span> allows
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application programs or users to access data files that reside on remote systems,
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and also allows remote systems to access data files on the local <span class="keyword">iSeries server</span>, as shown in <a href="#rbae5intrdf__rbae5systyps">Figure 1</a>.
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Any system that supports the DDM architecture as a source system can access
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data (if authorized to do so) on any other system to which it is attached.
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The attached system must support DDM as a <dfn class="term">target system</dfn> (the
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system that receives a request from another system to use one or more files
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located on the system). However, the source and target systems must support
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compatible subsets and levels of the DDM architecture.</p>
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<p>The folder management services (FMS) support allows personal computer users
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to access folders and documents that reside on an <span class="keyword">iSeries</span> target
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server. Remote systems that support Level 3.0 or Level 2.0 of the DDM architecture
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for the stream access method can access folders and documents on the local <span class="keyword">iSeries server</span>.</p>
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<p>DDM extends the file accessing capabilities of the <span class="keyword">iSeries server</span> database
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management support. In this topic collection, <dfn class="term">database management</dfn> refers
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to the system function that controls <strong>local</strong> file processing; that is,
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it controls access to data in files stored on the local <span class="keyword">iSeries server</span>,
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and it controls the transfer of that data to requesting programs on the same
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server.</p>
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<p><dfn class="term">Distributed data management</dfn> controls <strong>remote</strong> file processing.
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DDM enables application programs running on one <span class="keyword">iSeries server</span> to
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access data files stored on another server supporting DDM. Similarly, other
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systems that have DDM can access files in the database of the local <span class="keyword">iSeries server</span>. DDM makes it easier to distribute
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file processing between two or more servers.</p>
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<div class="fignone" id="rbae5intrdf__rbae5systyps"><a name="rbae5intrdf__rbae5systyps"><!-- --></a><span class="figcap">Figure 1. Source and target systems</span><br /><img src="rsll101.gif" alt="The systems that might be used as a target when an iSeries system is the source include another iSeries system, System/36, System/38, and other DDM-compatible systems." /><br /></div>
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<p>Systems that use DDM communicate with each other using the Advanced Program-to-Program
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Communication (APPC) support, Advanced Peer-to-Peer
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Networking<sup>®</sup> (APPN) support, or TCP/IP. See the <em>Communications Management</em> manual
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on the <a href="http://publib.boulder.ibm.com/iseries/v5r1/ic2924/rzaqhindex.htm">V5R1
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Supplemental Manuals</a> Web site<img src="www.gif" alt="Link outside information center" /> and the <a href="../rzahj/rzahjovr.htm">APPC, APPN, and HPR</a> topic for information needed to use
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APPC and APPN.</p>
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<p><dfn class="term">Folder management services</dfn> (FMS) allows local access to documents
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or folders that are on the <span class="keyword">iSeries server</span>.
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Personal computers might access folder management functions on the server
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by using DDM.</p>
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<div class="note"><span class="notetitle">Note:</span> Distributed data management for the IBM<sup>®</sup> Personal Computer uses the <span class="keyword">iSeries</span> portion of the <span class="keyword">iSeries Access Family</span> licensed
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program.</div>
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<p>As shown in <a href="#rbae5intrdf__rbae5srctgt1">Figure 2</a>, the server
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on which a user application issues a request involving a remote file is called
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a <dfn class="term">source system</dfn>. The server that receives the request for one
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of its files is called the <dfn class="term">target system</dfn>. A system can be both
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a source and target system for separate requests received at the same time.</p>
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<p>Using DDM, an application program can get, add, change, and delete data
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records in a file that exists on a target system. It can also perform file-related
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operations, such as creating, deleting, renaming, or copying a file from the
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target system to the source system. </p>
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<p>When DDM is in use, neither the application program nor the program user
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needs to know if the file that is needed exists locally or on a remote system.
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DDM handles remote file processing in essentially the same way as local file
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processing is handled on the local system, and the application program normally
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does not receive any indication of where the requested file is located. (However,
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in error conditions, messages are returned to the user that indicate, when
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necessary, that a remote system was accessed.) Informational messages about
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the use of target system files are included in the source system's job log.</p>
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<p>When DDM is to be used, only application programmers need
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to know where the file is located and, using control language (CL) commands
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outside of the high-level language (HLL) programs, they can control which
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file is used. However, the programmers can also choose to use specific recovery
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functions to handle certain communications failures; the HLL programs might
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need to be changed to include handling any such failure.</p>
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<p>Therefore, iSeries BASIC,
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ILE COBOL, ILE RPG, ILE C, and <span class="keyword">iSeries</span> programs
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that are compiled to process database files on the local server might not
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need to be changed or recompiled for DDM to process those same files when
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they are moved to or exist on a remote server.</p>
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<div class="fignone" id="rbae5intrdf__rbae5srctgt1"><a name="rbae5intrdf__rbae5srctgt1"><!-- --></a><span class="figcap">Figure 2. Move a program from a source
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to a target system</span><br /><img src="rsll102.gif" alt="This figure shows a program passing from an iSeries system to a DDM file and finally to the target iSeries system." /><br /></div>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><strong><a href="rbae5sytcomp.htm">System compatibility</a></strong><br />
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DDM can be used to communicate between systems that are architecturally different.</li>
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<li class="ulchildlink"><strong><a href="rbae5ddmfunc.htm">Overview of DDM functions</a></strong><br />
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This topic gives an overview of the types of DDM functions that can be done on a target server.</li>
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<li class="ulchildlink"><strong><a href="rbae5bascncp.htm">Basic DDM concepts</a></strong><br />
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This topic collection gives the basic concepts of DDM.</li>
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<li class="ulchildlink"><strong><a href="rbae5partsofddm.htm">Parts of DDM</a></strong><br />
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DDM consists of several parts to handle remote file processing among the systems using DDM.</li>
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<li class="ulchildlink"><strong><a href="rbae5advcncp.htm">Additional DDM concepts</a></strong><br />
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Most users of DDM will not need the information in the remainder of these topics; it is intended primarily for experienced programmers who need to know more about DDM.</li>
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<li class="ulchildlink"><strong><a href="rbae5exampleaccessmultiple.htm">Examples: Access multiple remote files with DDM</a></strong><br />
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These examples show a single application program using DDM to access multiple remote files.</li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rbae5kickoff.htm" title="This topic contains i5/OS distributed data management (DDM) concepts, information about preparing for DDM communications, and DDM-related programming information.">Distributed data management</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="rbae5prepddm.htm" title="There are several requirements that must be met for DDM to be used properly.">Prepare to use DDM</a></div>
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<div><a href="rbae5utlang.htm" title="This topic describes the language, utility, and application program support that is provided on the iSeries server for DDM.">Use language, utility, and application support for DDM</a></div>
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</div>
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</div>
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</body>
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</html>
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