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author Daniele Nicolodi <nicolodi@science.unitn.it>
date Wed, 23 Nov 2011 19:22:13 +0100
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1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
2 "http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd">
3
4 <html lang="en">
5 <head>
6 <meta name="generator" content=
7 "HTML Tidy for Mac OS X (vers 1st December 2004), see www.w3.org">
8 <meta http-equiv="Content-Type" content=
9 "text/html; charset=us-ascii">
10
11 <title>Retrieving LTPDA objects from a repository (LTPDA Toolbox)</title>
12 <link rel="stylesheet" href="docstyle.css" type="text/css">
13 <meta name="generator" content="DocBook XSL Stylesheets V1.52.2">
14 <meta name="description" content=
15 "Presents an overview of the features, system requirements, and starting the toolbox.">
16 </head>
17
18 <body>
19 <a name="top_of_page" id="top_of_page"></a>
20
21 <p style="font-size:1px;">&nbsp;</p>
22
23 <table class="nav" summary="Navigation aid" border="0" width=
24 "100%" cellpadding="0" cellspacing="0">
25 <tr>
26 <td valign="baseline"><b>LTPDA Toolbox</b></td><td><a href="../helptoc.html">contents</a></td>
27
28 <td valign="baseline" align="right"><a href=
29 "repo_explore.html"><img src="b_prev.gif" border="0" align=
30 "bottom" alt="Exploring an LTPDA Repository"></a>&nbsp;&nbsp;&nbsp;<a href=
31 "repo_gui.html"><img src="b_next.gif" border="0" align=
32 "bottom" alt="Using the LTPDA Repository GUI"></a></td>
33 </tr>
34 </table>
35
36 <h1 class="title"><a name="f3-12899" id="f3-12899"></a>Retrieving LTPDA objects from a repository</h1>
37 <hr>
38
39 <p>
40 <p>
41 Objects can be retrieved from the repository either by specifying an object ID or a collection ID. The LTPDA
42 Toolbox provides class construtors to retrieve objects. In additon, to retrieve a collection of objects, the <tt>collection</tt> class
43 can be used.
44 </p>
45 <br>
46 <h2>The retrieval process</h2>
47 <p>
48 When an object is retrieved, the following steps are taken:
49 <ol>
50 <li>The object type for the requested ID is retrieved from the <tt>objmeta</tt> table</li>
51 <li>A call is made to the appropriate class constructor</li>
52 <li>The class constructor retrieves the XML string from the objs table</li>
53 <li>The XML string is then converted into an XML Xdoc object</li>
54 <li>The Xdoc object is then parsed to recreate the desired object</li>
55 </ol>
56 </p>
57
58 <br>
59 <h2>Retrieving objects</h2>
60
61 <p>
62 To retrieve an object, you must know its object ID, or the ID of the collection that contains that object. If you don't know the
63 class of the object, you can use the <tt>collection</tt> class as a container, as follows:
64 <div class="fragment"><pre>
65 >> a = collection(plist('hostname', 'localhost', 'database', 'ltpda_test', 'id', 1))
66
67 ** Connection status:
68 LWB: Disconnected from localhost/ltpda_test as hewitson
69 ---- collection 1 ----
70 name: none
71 num objs: 1
72 01: ao | New Block/tsdataNdata=[10x1], fs=1, nsecs=10, t0=1970-01-01 00:00:00.000
73 description:
74 UUID: 9ec7a613-9442-4451-9b40-af18f4afea00
75 ----------------------
76 </pre></div>
77 </p>
78 <p>
79 If you already know the class of the object (for example, <tt>ao</tt>), you can directly call the class constructor method:
80 <div class="fragment"><pre>
81 <span class="comment">% Define the hostname and database</span>
82 hostname = <span class="string">'localhost'</span>;
83 database = <span class="string">'ltpda_test'</span>;
84
85 <span class="comment">% Retrieve the object</span>
86 q = ao(plist(<span class="string">'hostname'</span>, hostname, <span class="string">'database'</span>, dbname, <span class="string">'ID'</span>, 12));
87 </pre></div>
88 </p>
89
90 <br>
91 <p>
92 Multiple objects can be retrieved simultaneously by giving a list of object IDs. For example
93 <div class="fragment"><pre>
94 >> a = ao(plist('hostname', 'localhost', 'database', 'ltpda_test', 'id', [1 2 3]))
95 </pre></div>
96 </p>
97 <br>
98 <h2>Retrieving object collections</h2>
99 <p>
100 Collections of objects can be retrieved by specifying the collection ID. The following script retrieves a collection:
101 <div class="fragment"><pre>
102 >> a = collection(plist('hostname', 'localhost', 'database', 'ltpda_test', 'cid', 1))
103 </pre></div>
104 The output is a <tt>collection</tt> object containing the objects retrieved.
105 </p>
106
107 <h2>Retrieving binary objects</h2>
108 <p>The retrieval process may be speeded up by taking advantage of the fact that the objects are stored in the databases also in binary form.
109 This can be achieved by using the parameter 'binary', that will build the object from the corresponding binary representation, if
110 stored in the database.
111 <div class="fragment"><pre>
112 <span class="comment">% Retrieve the collection</span>
113 q = ao(plist(<span class="string">'hostname'</span>, hostname, <span class="string">'database'</span>, dbname, <span class="string">'ID'</span>, 12, <span class="string">'binary'</span>, <span class="string">'yes'</span>));
114 </pre></div>
115 If the binary representation is not in the database, the object will be built from the xml one.
116 </p>
117
118 </p>
119
120 <br>
121 <br>
122 <table class="nav" summary="Navigation aid" border="0" width=
123 "100%" cellpadding="0" cellspacing="0">
124 <tr valign="top">
125 <td align="left" width="20"><a href="repo_explore.html"><img src=
126 "b_prev.gif" border="0" align="bottom" alt=
127 "Exploring an LTPDA Repository"></a>&nbsp;</td>
128
129 <td align="left">Exploring an LTPDA Repository</td>
130
131 <td>&nbsp;</td>
132
133 <td align="right">Using the LTPDA Repository GUI</td>
134
135 <td align="right" width="20"><a href=
136 "repo_gui.html"><img src="b_next.gif" border="0" align=
137 "bottom" alt="Using the LTPDA Repository GUI"></a></td>
138 </tr>
139 </table><br>
140
141 <p class="copy">&copy;LTP Team</p>
142 </body>
143 </html>