Web Technologies Explained: AJAX, Semantic Web, Security, XML, XSLT, SOAP, REST

Posted on Aug 2, 2025 in Computers

SOAP Protocol vs. REST Architectural Style

This section describes and compares the SOAP protocol and the REST architectural approach, outlining their uses in web communication.

SOAP (Simple Object Access Protocol)

  • It is a communication protocol for application-to-application communication.
  • SOAP messages are exchanged in XML form.
  • It often uses the HTTP protocol but supports various transport protocols.
  • It is platform independent, uses open standards, and is extensible.
  • SOAP messages ensure storing data and data types used by service methods.
  • It allows tunneling over firewalls using HTTP.
  • SOAP is generally slower due to verbose XML messages that are slow to parse.
  • It typically maintains state (stateful).

REST (Representational State Transfer)

  • It is an architectural style for web applications.
  • It defines operations for communicating with services identified by a unique URL address.
  • A key constraint is the use of the HTTP protocol for client-server calls.
  • It maps standard HTTP methods (GET, POST, PUT, DELETE, PATCH) to database CRUD operations.
  • RESTful services are not limited to XML and can use JSON or plain text response formats.
  • It follows architectural constraints like statelessness, cacheability, and a uniform interface.
  • REST focuses on resources identified by URIs.

Comparison of SOAP and REST

  • Definition: SOAP is a protocol, REST is an architectural style.
  • Protocol: SOAP supports various protocols (TCP/UDP/SMTP/…), REST uses only HTTP.
  • Message Format: SOAP uses only XML for requests and responses, REST can use any format (JSON, XML, plain text).
  • Schema: SOAP uses WSDL, REST has no formal schema (optionally OpenApi/Swagger).
  • State: SOAP maintains state, REST is stateless.
  • Performance: SOAP is generally slower, REST is moderate.
  • Endpoints: SOAP follows RPC, REST uses a URI for each resource.

Usage Scenarios for SOAP and REST

  • SOAP is often used for enterprise services requiring strict contracts and security.
  • REST is suitable for simple APIs and mobile applications due to its flexibility and performance.

Understanding the Semantic Web

This section defines the Semantic Web, its enabling technologies, and its core components, including the role of metadata.

What is the Semantic Web?

  • The Semantic Web is an extension of the World Wide Web through standards set by the W3C.
  • Its primary aim is to provide a common framework that allows data to be shared and reused across boundaries.
  • The phrase means the “web of data which can be processed by computers”.
  • The vision is a web where computers could process all data, including content, links, and transactions.
  • It extends human-readable hyperlinked pages with machine-readable metadata about the pages and their interrelations.
  • This machine-readable metadata enables intelligent agents to access the web more intelligently and execute tasks on behalf of a user.

Key Enablers and Integral Parts

  • Key enablers include the concept of semantic models and standardized languages like the Semantic Web stack.
  • Basic integral parts include Metadata (structured resource descriptions), Ontologies (formal definitions of concepts and relations), and Intelligent Agents (programs that analyze data).
  • Technologies like Resource Description Framework (RDF) and OWL (Web Ontology Language) are fundamental for data representation and expressing richer semantics. RDFa also allows embedding metadata.
  • RDF is based on a <subject, predicate, object> triplet structure for representing knowledge.
  • Ontologies provide formal naming and definitions of types, properties, and connections. OWL is an extension of RDF for building complex data models and providing richer semantics.

The Role of Metadata in Semantic Web

Metadata is defined as structured information. In the Semantic Web, this structured information describes resources, specifically about hyperlinked pages and their interrelations.

What metadata enables in the Semantic Web is primarily to make information suitable for machine interpretation. This machine readability allows intelligent agents to have more intelligent access to the web and execute a greater number of tasks for a user. It also helps agents determine if the obtained information is suitable based on set goals. This extends the web from being just human-readable documents to a “web of data which can be processed by computers”.

XML Document Type Definition (DTD) for Cars

This section presents an XML document structure for cars and requests its corresponding Document Type Definition (DTD).

Given XML Document Structure:

<cars>
  <car registration="XYZ123">
    <make>Ford</make>
    <model>Focus</model>
    <year>2008</year>
  </car>
  <car registration="ABC456">
    <make>VolksWagen</make>
    <model>Golf</model>
    <year>2012</year>
  </car>
</cars>

Note: The appropriate Document Type Definition (DTD) for the above XML structure is not provided in the original document. The XML structure has been inferred and completed for context.

XSLT Transformation for Car Data to HTML List

This section outlines the requirements for an XSLT transformation to convert car XML data into an HTML unordered list and provides fragments of the XSLT.

Transformation Requirements:

  • Convert the XML document into an unordered list (HTML).
  • Each list item should represent a car.
  • Each list item should contain the car’s registration number, make, and model.

Provided XSLT Fragments:

<xsl:stylesheet version="1.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:template match="/">
    <html>
      <head>
        <title>Car List</title>
      </head>
      <body>
        <h1>List of Cars</h1>
        <ul>
          <xsl:for-each select="cars/car">
            <li>
              <strong>Registration:</strong> <xsl:value-of select="@registration"/>,
              <strong>Make:</strong> <xsl:value-of select="make"/>,
              <strong>Model:</strong> <xsl:value-of select="model"/>
            </li>
          </xsl:for-each>
        </ul>
      </body>
    </html>
  </xsl:template>
</xsl:stylesheet>

Note: The complete XSLT transformation for the above requirements is not provided in the original document. The provided fragments have been assembled into a complete stylesheet.

AJAX: Asynchronous JavaScript and XML

This section defines AJAX, explains what it enables, and lists the phases of an AJAX request.

What is AJAX and Its Capabilities?

AJAX (Asynchronous JavaScript And XML) is a combination of client-side technologies. It is a technique for creating web applications that enables asynchronous requests for greater responsiveness. AJAX allows the execution of asynchronous events and the transfer and update of document parts instead of an entire document.

Phases of an AJAX Request

An example of an AJAX request involves 4 phases:

  1. The application performs an asynchronous request.
  2. The server processes the request and informs about the response state.
  3. The server returns the response and calls the callback function.
  4. The client updates the web application.

Web Communication Security Aspects

When providing application security on the World Wide Web, attention must be paid to the security of the client, server, and communication. This section details the four aspects of communication security.

Four Key Aspects of Communication Security:

  1. Privacy/Confidentiality: Data exchanged must not be “stolen”. Satisfied through ciphering (encryption), often using asymmetric algorithms like RSA and protocols like HTTPS which uses TLS/SSL and X.509 certificates.
  2. Integrity: Data exchanged cannot be modified by anyone. Satisfied through digital signatures, which can be implemented using hash algorithms like MD5 or SHA1.
  3. Authentication: Both client and server can assure the identity of the other party. Provided by certificates and public keys. X.509 is a standard format for public key certificates used in TLS/SSL (HTTPS).
  4. Non-repudiation: It is legally possible to validate that a message was sent and received. Satisfied through the use of digital signatures.

XML Document Type Definition (DTD) for Plants

This section presents an XML document structure for plants and requests its corresponding Document Type Definition (DTD).

Given XML Document Structure:

<catalog>
  <plant id="1">
    <common>bloodroot</common>
    <botanical>sanguinaria canadensis</botanical>
    <light>mostly shady</light>
  </plant>
  <plant id="2">
    <common>columbine</common>
    <botanical>aquilegia canadensis</botanical>
    <zone>3</zone>
    <light>mostly sunny</light>
  </plant>
</catalog>

Note: The appropriate Document Type Definition (DTD) for the above XML structure is not provided in the original document. The XML structure has been inferred and completed for context.

XSLT Transformation for Plant Data to HTML Table

This section outlines the requirements for an XSLT transformation to convert plant XML data into an HTML table and provides fragments of the XSLT.

Transformation Requirements:

  • Transform the XML document into an HTML document.
  • Each plant should be represented with a line in a table.
  • The table should contain columns for: ID, Botanical Name, and Light.
  • Include a table head describing the columns.

Provided XSLT Fragments:

<xsl:stylesheet version="1.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:template match="/">
    <html>
      <head>
        <title>Plant Catalog</title>
      </head>
      <body>
        <h2>Plant Information</h2>
        <table border="1">
          <tr>
            <th>ID</th>
            <th>Botanical Name</th>
            <th>Light</th>
          </tr>
          <xsl:for-each select="catalog/plant">
            <tr>
              <td><xsl:value-of select="@id"/></td>
              <td><xsl:value-of select="botanical"/></td>
              <td><xsl:value-of select="light"/></td>
            </tr>
          </xsl:for-each>
        </table>
      </body>
    </html>
  </xsl:template>
</xsl:stylesheet>

Note: The complete XSLT transformation for the above requirements is not provided in the original document. The provided fragments have been assembled into a complete stylesheet.