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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-27A393D5-C7DF-5541-855A-2CB0E4C46D6D" xml:lang="en"><title>The

    13 DBMS server</title><shortdesc>Describes the features of the DBMS server.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    14 <p>A session with the DBMS server provides the basis for sharing databases

    15 with other threads; the DBMS server allows shared read/write access to databases

    16 by multiple clients.</p>

    17 <p>A session with the DBMS server is set up through an instance of the <codeph>RDbs</codeph> class.

    18 The behaviour of this class is similar to other session classes, for example,

    19 the file server session class, <codeph>RFs</codeph>.</p>

    20 <p>A client opens a connection with the DBMS server using the <codeph>Connect()</codeph> member

    21 function of <codeph>RDbs</codeph> and closes the connection by calling <codeph>Close()</codeph> on <codeph>RDbs</codeph>.</p>

    22 <p>Some useful points to note:</p>

    23 <ul>

    24 <li id="GUID-2CBE14E2-B9B9-59C0-B4A2-ED0A4C4DCFF7"><p>a thread can open any

    25 number of simultaneous connections to the DBMS server</p> </li>

    26 <li id="GUID-B9F8CA69-3594-5692-9B39-19800D8E8AB8"><p>a session can be used

    27 to open any number of databases.</p> </li>

    28 <li id="GUID-29CF3CF7-0786-5454-B79D-BD4B451701F1"><p>the same database can

    29 be opened many times within a single session; each such database object behaves

    30 independently with regard to transactions. </p> </li>

    31 <li id="GUID-9436A9F0-D007-5ED6-8E96-713F44EEF4A4"><p>a database cannot be

    32 opened for client-side read access and client-server write access at the same

    33 time; if write access is required by one client, then all clients must use

    34 the DBMS server.</p> </li>

    35 <li id="GUID-D52B72B2-699C-561A-B290-9FD1AEA0790F"><p>a session must be kept

    36 open until all DBMS objects opened through it have been closed.</p> </li>

    37 </ul>

    38 <p>Shared databases support all DBMS API functionality except database creation

    39 and changing the security key:</p>

    40 <ul>

    41 <li id="GUID-EAD7BB8E-5E08-50B7-A158-2125D32E1539"><p>databases should only

    42 be shared once they have a fully constructed schema, otherwise clients may

    43 attempt to access a half-created database.</p> </li>

    44 <li id="GUID-B65A6BA3-55EA-555D-9FBF-F13D8B916694"><p>using the <codeph>ChangeSecurity()</codeph> member

    45 function of <codeph>RDbDatabase</codeph> to change the security key for a

    46 secure database makes no sense if the database is currently shared.</p> </li>

    47 </ul>

    48 <p>The client server interface offers utility functions which allow the client

    49 to check the number of allocated DBMS objects.</p>

    50 <p>The interface also offers heap debugging support for the server's heap.</p>

    51 </conbody></concept>