Tuesday, June 6, 2017

Web Services Introduction

Web Service definition

  • A web service is a distributed software whose components can be deployed and executed on distinct devices.
  • A web service consists of a service (a.k.a. producer) and a client (a.k.a. consumer or requester).

Web Service over HTTP

  • A web service is an application typically running over HTTP.
  • A web service over HTTP is a web service that uses the HTTP as transport, HTTP messages are infrastructure.

Web Service architecture

  • The architecture of a simple web service is a client and a server.
  • The architecture of a complicated web service have many clients and a service composed of other services.
    • for example, an e-commerce service can be composed of multiple code components (each hosted on a separate web server) and any combination of PCs, tablets, mobile phones and other networked devices may host programs that make requests to the service.

Web services come in two flavors: SAOP-based and REST-style.

  • SOAP is an XML dialect that specifies the structure of XML documents that count as SOAP envelopes
  • A REST-style service is one that treats HTTP not only as a transport infrastructure but also as a set of guidelines for making service requests and responses.

Web service features

  • Web service major attractiveness is interoperability: clients and services can interact despite differences in programming languages, operating systems and hardware platforms.
  • XML and JSON are web service data interchange formats that provide an intermediary level and handle the differences in data types between different programming languages.

Tuesday, May 9, 2017

How to validate an xml document against a schema

STEP 1: Create the XML

To create a new XML file, start eclipse IDE and choose File->New->Other->XML file->Create XML file from XML template.
Model the data of interest in the XML file. In my case, I have created the following XML.

The teams.xml file

<?xml version="1.0" encoding="UTF-8"?>
<team>
 <name>the great team</name>
 <description>these team was recruited by google to develop a secret product</description>
 <developers>
  <developer role="frontend">
   <name>John Carrot</name>
  </developer>
  <developer role="backend">
   <name>Joshua Allock</name>
  </developer>
  <developer role="frontend">
   <name>Brendan Tich</name>
  </developer>
 </developers>
</team>

Tuesday, March 14, 2017

XML Schema Primer

1 Introduction

Basic Concepts: The Purchase Order (§2) covers the basic mechanisms of XML Schema. It describes how to declare the elements and attributes that appear in XML documents, the distinctions between simple and complex types, defining complex types, the use of simple types for element and attribute values, schema annotation, a simple mechanism for re-using element and attribute definitions, and nil values.

Advanced Concepts I: Namespaces, Schemas & Qualification (§3), explains the basics of how namespaces are used in XML and schema documents.

2 Basic Concepts: The Purchase Order

The purpose of XML schemas

  • a schema defines a class of XML documents (is a description of an XML document)
  • an instance document is an XML document that conforms to a particular schema

The instance document, the po.xml file, describes a purchase order that may be generated by a product ordering application.

Example
The Purchase Order, po.xml
<?xml version="1.0"?>
<purchaseOrder orderDate="1999-10-20">
   <shipTo country="US">
      <name>Alice Smith</name>
      <street>123 Maple Street</street>
      <city>Mill Valley</city>
      <state>CA</state>
      <zip>90952</zip>
   </shipTo>
   <billTo country="US">
      <name>Robert Smith</name>
      <street>8 Oak Avenue</street>
      <city>Old Town</city>
      <state>PA</state>
      <zip>95819</zip>
   </billTo>
   <comment>Hurry, my lawn is going wild!</comment>
   <items>
      <item partNum="872-AA">
         <productName>Lawnmower</productName>
         <quantity>1</quantity>
         <USPrice>148.95</USPrice>
         <comment>Confirm this is electric</comment>
      </item>
      <item partNum="926-AA">
         <productName>Baby Monitor</productName>
         <quantity>1</quantity>
         <USPrice>39.98</USPrice>
         <shipDate>1999-05-21</shipDate>
      </item>
   </items>
</purchaseOrder>

The purchase order's elements have simple types or complex types

  • the purchase order consists of a main element purchaseOrder and the subelements {shipTo, billTo, comment, items}.
  • subelements can contain other subelements or data
  • elements that contain subelements or carry attributes are said to have complex types
  • elements that contain numbers, strings, dates and no subelements are said to have simple types, attributes always have simple types

Where to find the definitions of the types in the instance document

  • the complex types in the instance document are defined in the schema for purchase orders
  • the simple types in the instance document are defined either in the schema for purchase orders or are part of the built-in simple types of XML Schema

What is the association between the instance document and the the purchase order schema?

  • an instance document does not need to refer to a schema
  • the purchase order does not reference the purchase order schema