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<p class="head">BIRT FAQ</p>
<p class="subhead">Report Layout</p>
<h1>Report Object Model (ROM)</h1>
<h2>Q: What is the ROM?</h2>
<p>ROM stands for &quot;Report Object Model.&quot; It is the model (or
specification) behind BIRT report elements. Just as HTML, CSS and SOAP are
standards separate from an implementation, so ROM is a model separate from the
BIRT implementation.</p>
<p>ROM is the model behind the palette items, property dialogs,
methods and so on. ROM consists of a set of core elements, and rules for adding
extended elements.</p>
<p>Elements can have properties. Properties have a type. Property
types include simple ones such a string, number, dimension and so or. Property
types also include complex ones such as structures, lists, and lists of
structures. For example, static text is defined as a structure with text and a
resource key for internationalization.</p>
<p>Elements can fit together using &quot;slots&quot;. Each element has named
slots. For example, the report element has slots for the layout (body), for
styles, and so on.</p>
<p>Elements can have methods &amp; expressions (code). These are
specialized forms of properties.</p>
<p>In a later release, elements will be able to inherit from another
element. This will allow reuse. For example, you can define a data source in a
library, and use it in multiple report designs.</p>
<p>ROM provides styles and style properties. ROM's style system is
based on CSS, extended for use within a report. Users can create their own
styles, or can use many predefined styles. Predefined styles in ROM select
specific report items. For example, the &quot;report&quot; style sets defaults for the
entire report. As in CSS, styles cascade. Style information set on a container
element cascades to its contents.</p>
<p>To learn more about ROM, read the ROM Specifications located in
the <a href="../ref">reference area</a> of this web site.</p>
<h2>Q: What is the XML design file?</h2>
<p>BIRT stores your report design in a &quot;design file.&quot; This file is
in XML format and has a &quot;.rptdesign&quot; suffix. The XML design file is created by
the BIRT designer and directly executed by the BIRT engine; there is no
compilation step.</p>
<h2>Q: What is the ROM schema?</h2>
<p>The BIRT XML design file is defined by an XML schema. At present,
the schema is located in the BIRT source code in the
org.eclipse.birt.report.model project in the src\org\eclipse\birt\report\model\parser\design.xsd
file. Eventually, it will move to a well-defined location on the Eclipse web
site.</p>
<p>The schema is designed to allow extensions. The schema defines
syntax that allows extensions to be added to BIRT without making changes to the
actual schema. For example, an extended item uses the following tag:</p>
<pre class="code-block">&lt;extended-item name=&quot;extension&quot;&gt;</pre>
<p>Properties are in a generic form:</p>
<pre class="code-block">&lt;property name=&quot;propName&quot;&gt;value&lt;/property&gt;.</pre>
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<p>In this sense, the schema describes a syntax for representing
report elements in general. The schema does not list the properties, for
example; that is defined in a separate rom.def file that is derived from the ROM
specification.</p>
<h2>Q: What is rom.def?</h2>
<p>The ROM schema defines the syntax for the XML design file. The specific set of ROM-defined elements, their slots, and their properties are defined by a separate internal metadata file called rom.def. This file is in the BIRT source code in the org.eclipse.birt.report.model in the src\org\eclipse\birt\report\model\elements\rom.def file.</p>
<p>Rom.def contains the information that drives the generic property sheet by defining properties and property types. It also describes JavaScript objects defined by BIRT and other meta-data.</p>
<p>The metadata subsystem of the BIRT model provides a Java API to access this information.</p>
<h1>Data Display</h1>
<h2>Q: How do I display page numbers in HTML or PDF?</h2><p>BIRT uses Apache FOP to convert a report to PDF. FOP does
pagination and assigns page numbers. As a result, there is no JavaScript
expression you can use to get the current page number. Instead, BIRT will add a
new &quot;page number&quot; element. It will include a special marker string that tells
BIRT or FO where to insert the page number. BIRT will interpret the string when
converting to HTML, and will convert the marker to the required FO syntax when
converting to PDF using FOP.</p>
<p>The element will allow you to say something like:</p>
<pre class="code-block">Page $page of $count</pre>
<p>At runtime, this will be replaced by:</p>
<pre class="code-block">Page 1 of 5</pre>
<p class="caution"><span class="caution-head">Release 1.0M2 Note:</span> The
page number element has not yet been released. Syntax is still subject to
change.</p>
<h2>Q: How do I display today's Date?</h2>
<p>Add a data item. For the expression, enter:</p>
<pre class="code-block">new Date( );</pre>
<p>Then, in the Format page of the Property Editor, choose the date
format you prefer, such as Medium Date for a display of Apr 15, 2005.</p>
<h2>Q: How do I display the row number?</h2>
<p>Suppose you want to display a list of items, along with the row
number of each. BIRT provides the row variable that gives data for the current
data row. row[0] provides the 0-based row index. You can display a 1-based count
as follows:</p>
<pre class="code-block">row[0] + 1;</pre>
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