A Gentle Introduction to DDI - What's in it for me?

Jim Jacobs University of California, San Diego Wendy Thomas University of Minnesota

List of handouts

• Module description

• DDI track

• Guide to sourceforge

• List of websites and documents

• List of people, e-mails

Quick Review: HTML / XML

< >stuff</>

Quick Review: HTML / XML

The Sun Also Rises

Quick Review: HTML / XML

<i>The Sun Also Rises</i>

Quick Review: HTML / XML

<i>The Sun Also Rises</i>

<title>The Sun Also Rises</title>

Quick Review: HTML / XML

<i>The Sun Also Rises</i>

<title>The Sun Also Rises</title>

HTML documents can impart appearance. XML documents impart meaning.

Quick Review: HTML / XML

• <author>• <au>• <pi>

But…where are the rules for <i> and <title>??

Why not <ti> or <t>?

What do we use?

Quick Review: HTML / XML

• <author>• <au>• <pi>

But…where are the rules for <i> and <title>??

Why not <ti> or <t>?

What do we use?The vocabulary and syntax are defined in a special document.

There are two kinds of these special documents:

Document Type Definition (DTD)Schema

Quick Review: HTML / XML

HTML is defined in a DTD:

http://www.w3.org/TR/html4/sgml/dtd.html

<!ENTITY % fontstyle "TT | I | B | BIG | SMALL">

DDI

• DDI 1 and 2 were defined by a DTDhttp://www.icpsr.umich.edu/DDI/Version2-1.dtd

• DDI 3 is defined by a Schemahttp://cvs.sourceforge.net/viewcvs.py/*checkout*/ddi-alliance/ddi/w3c/Version2-1.xsd

DTDs and Schemas

HTML document

HTML DTD

HTML document

DTDs and Schemas

DDI 2 document

DDI 2 DTD

DDI 2 document

DTDs and Schemas

DDI 2 document

DDI 2 DTD

DDI 2 document

DDI 3.0Document

DDI 3.0 Schema

DDI 3.0Document

What is the advantage of Schema over DTD?

• XML as a document format

• XML as a data format

• DTDs are more useful for describing XML document formats

• Schemas are more useful for describing XML data formats.

What is the advantage of Schema over DTD?

Despite the intentions of XML's inventors, who mostly envisioned XML as a format for web pages and other narrative documents to be read by people, the most common applications of XML today involve the storage and transmission of information for use by different software applications and systems.

-- XML in a Nutshell, Elliotte Rusty and W. Scott Means

What is the advantage of Schema over DTD?

• Schemas make it easier to treat metadata like data.

• The focus becomes on the content (e.g., the variables, questions, question groups, concepts, etc.), not the application (e.g. SAS, SPSS, PDF…).

A little vocabulary…

• Elements

<table></table>

• Attributes

<a href=“http://nytimes.com”></a>

A little vocabulary…

• Elements

<title></title>

• Attributes

<recGrp rectype="Person record">

A little vocabulary…

• Data types– string – decimal– integer – boolean – date – time

A little vocabulary…

• Namespace

A means of distinguishing between elements and attributesfrom different XML vocabularies that have the same name.

<table> <tr> <td>Apples</td> <td>Bananas</td> </tr></table>

<table> <name>African Coffee Table</name> <width>80</width> <length>120</length></table>

A little vocabulary…

• Namespace

A means of distinguishing between elements and attributesfrom different XML vocabularies that have the same name.

<h:table> <h:tr> <h:td>Apples</h:td> <h:td>Bananas</h:td> </h:tr></h:table>

<f:table> <f:name>African Coffee Table</f:name> <f:width>80</f:width> <f:length>120</f:length></f:table>

What are the advantages of Schema over DTD?

• Written in XML• Support for data types• Support for namespaces• Better control over information (e.g., minimum and

maxium values)• Support for XML as a data format• Modularity• Machine-Actionable

So… what can we do with DDI 3.0?

• Better manage our local archives with the Archive Module.

• Better manage different (and multiple) physical formats and/or record subsets.

• Transform information from XML into rss, rdf, pdf, html, xml, SPSS, etc.

• Record information on the lifecycle of research [versioning information]