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3. Turning web data into objects

a. XML - Extended Markup Language

Languages such as Java, C++, Perl and Python, are designed to allow networked objects to communicate with one another. The nature of the data must be hard-coded into the programs, or into the database definition. 

Another approach to data interchange between objects is XML. XML  is a protocol for defining datafile formats. It is not a file format per se. Rather,  XML standardizes how data files are defined.

Although XML is still an evolving set of protocols, several components are critical to XML:

  1. Data Definition
  2. XML - an instance of data following the specifications of the DTD or schema
    Usually, an application will check each XML file to make sure it conforms to the DTD. If valid, the XML file is read, and the corresponding data objects are created.
    EXAMPLE: The pea disease resistance response gene DRR206 is found in UniProtKB in entry P13240.
  3. XSL - XML stylesheet language
    One of the most important uses for XML is as an alternative to HTML. HTML is limited to displaying text in a fairly simple fashion. XML allows the creation of rich data types. However, XML files, unlike HTML, don't specify how data are to be displayed in a browser. Therefore, XML stylesheets can be written for each type of XML file, providing a consistent structure to XML document presentation. Most of the major web browsers (IE, Mozilla, Firefox) provide at least some XML support.


a -In this example, an application has been programmed to read a specific type of XML file. An object is created within the application based on the specifications in the XML file.

b - Conversely to a, an object in the application is translated to an XML representation, and written to a file.

c - This is a complex example. Data from a binary database is written to an XML file. At top, an client program, specialized for this particular XML data type, reads the XML and creates an object.

If a stylesheet exists for this XML data type, a browser can import the same XML file and render it as a Web page. In this case, a complex page, consisting of text, graphics, and a Java applet, is rendered.

XML is still evolving! Use with caution!
The standards for XML are still under development, particularly with regard to XSL stylesheets, XML schemas, and XML browsers. As well, in particular fields, numerous mutually incompatible DTDs may exist for the same type of data object! For example, an XML file for a DNA sequence or a protein, produced by one program, may be unreadable by another program, even though both programs can read XML.

Most of the widely-used languages (Java, C++, Python, Perl) have extensive libraries for reading, writing and manipulating XML objects.

b. Ontologies - relationships beteween data objects

Open Biomedical Ontologies []
Gene Ontology []

Controlled vocabulary - A controlled vocabulary is an established list of standardized terminology for use in indexing and retrieval of information. In a controlled vocabulary, every object has an agreed-upon name, for which there may be many synonyms. Regardless of the synonym used, it is possible to find the name used by the controlled vocabulary.

Ontology - "... an explicit specification of some topic. For our purposes, it is a formal and declarative representation which includes the vocabulary (or names) for referring to the terms in that subject area and the logical statements that describe what the terms are, how they are related to each other, and how they can or cannot be related to each other. Ontologies therefore provide a vocabulary for representing and communicating knowledge about some topic and a set of relationships that hold among the terms in that vocabulary (From the Stanford Knowledge Systems Lab)."

Ontologies are designed as Directed Acyclic Graphs (DAG). DAGs have the following properties:

In an ontology, relationships between nodes are defined. Usually, only a small number of relationships need to be defined. This will be illustrated using Gene Ontology as an example.

Gene Ontology

The goal of Gene Ontology is to create a formal description of the relationships among genes and proteins and their cellular roles. The current GO defines three high-level categories: Biological Process, Molecular Function and Cell Component.

As illustrated above, relationships between objects are also defined.

The entire GO tree can be viewed or searched at

Gene ontologies are often cited in sequence and genome annotation.

Example:  Annotation extracted from GenBank protein entry EFN87342:

LOCUS       EFN87342                 566 aa            linear   INV 13-MAR-2015
DEFINITION  Laccase, partial [Harpegnathos saltator].
VERSION     EFN87342.1

. . .
. . .
     CDS             1..566
                     /note="GO_function: GO:0005507 - copper ion binding
                     [Evidence IEA];
                     GO_function: GO:0016491 - oxidoreductase activity
                     [Evidence IEA];
                     GO_process: GO:0055114 - oxidation reduction [Evidence

There are three GO references: to copper ion binding, oxidoreductase activity and oxidation reduction. All three are probably closely related.

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Lecture 9, part 3 of 4
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