What is XML?

 What is XML?

• XML (eXtensible Markup Language)

  • Universal language (notation) for describing structured data using text with tags

  • The data is stored together with the meta-data about it

  • Used to describe other languages (formats) for data representation

• XML looks like HTML

  • Text based language, uses tags and attributes

 What is XML?

• Worldwide standard

  • Supported by the W3C - www.w3c.org

• Independent of operating system and programming languages

<?xml version="1.0"?>
<library name=".NET Developer's Library">
  <book>
    <title>Professional C# 4.0 and .NET 4</title>
    <author>Christian Nagel</author>
  </book>
  <book>
    <title>Silverlight in Action</title>
    <author>Pete Brown</author>
  </book>
</library>

 XML and HTML

• Similarities between XML and HTML

  • Both are text based notations

  • Both use tags and attributes

• Differences between XML and HTML

  • HTML is a language, and XML is a syntax for describing other languages

  • HTML describes the formatting of information, XML describes structured information

  • XML requires the documents to be well-formatted

 Formatting

• Well-formatted XML:

  • All tags should be closed in the correct order of nesting

  • Attributes should always be closed

  • The document should contain only one root element

  • Tag and attribute names retain certain restrictions

<?xml version="1.0"?>
<library name=".NET Developer's Library">
  <book>
    <title>Professional C# 4.0 and .NET 4</title>
    <author>Christian Nagel</author>
  </book>
</library>

 Advantages

• Advantages of XML:

  • XML is human readable (unlike binary formats)

  • Any kind of structured data can be stored

  • Data comes with self-describing meta-data

  • Custom XML-based languages can be developed for certain applications

  • Information can be exchanged between different systems with ease

  • Unicode is fully supported

 Disadvantages

• Disadvantages of XML:

  • XML data is bigger (takes more space) than in binary formats

    • More memory consumption, more network traffic, more hard-disk space

  • Decreased performance

    • Need of parsing / constructing the XML tags

  • XML is not suitable for all kinds of data

    • E.g. graphics, images and video clips

Working with XML

 XML Parsers

• XML parsers are programming libraries that make the work with XML easier

• They serve for:

  • Extracting data from XML documents

  • Modifying existing XML documents

  • Building new XML documents

  • Validating XML documents by given schema

  • Transforming XML documents

 XML Parsers

• They have several working models:

  • DOM (Document Object Model)

    • Represents XML documents as a tree in the memory

    • Allows processing and modifying the document

  • SAX (Simple API for XML Processing)

    • Reads XML documents consequently element by element

    • Event-driven API

    • Allows analyzing the read portions at each step

  • StAX (Streaming API for XML)

    • Like SAX but works in "pull" mode

 XML Parser in .NET

• The DOM parser provides few important classes:

  • XmlDocument - Represents the DOM tree

    • Usually contains two elements:

      • Header part (prolog)

      • The root element of the XML document

  • XmlNode

    • Abstract base class for all nodes in a DOM tree

  • XmlElement

    • Represents a XML element

  • XmlAttribute

    • Represents an attribute of an XML tag

 XML Parser in .NET - Example

XmlDocument doc = new XmlDocument();
doc.Load("library.xml");

XmlNode rootNode = doc.DocumentElement;
Console.WriteLine("Root node: {0}", rootNode.Name);

foreach (XmlAttribute atr in rootNode.Attributes)
{
  Console.WriteLine("Attribute: {0}={1}", atr.Name, atr.Value);
}

var children = rootNode.ChildNodes;

Console.WriteLine("Book title = {0}", children["title"].InnerText);
Console.WriteLine("Book author = {0}", children["author"].InnerText);
Console.WriteLine("Book isbn = {0}", children["isbn"].InnerText);

 The XmlNode Class

• Working with siblings and children

  • PreviousSibling / NextSibling – returns the left / right node to the current

  • FirstChild / LastChild – returns the first / last child of the current node

  • Item (indexer [] in C#) – returns the child of the current node by its name

• Working with the current node:

  • Name – returns the name of the node (element, attribute …)

  • Value – gets the node value

 The XmlNode Class

• Changing of the current node:

  • AppendChild(…) / PrependChild(…)

    • Inserts new child after / before all other children of the current node

  • InsertBefore(…) / InsertAfter(…)

    • Inserts new child before / after given inheritor

  • RemoveChild(…) / ReplaceChild(…)

    • Removes / replaces given child

What is JSON?

 What is JSON?

• JSON (JavaScript Object Notation) is a lightweight data format

  • Human and machine-readable

  • Based on the way to create objects in JS

  • Platform independent - can be used with any programming language

{
  firstName: "John", 
  lastName: "Smith", 
  age: 25,
  phoneNumbers: [
    { type: "home", number: "212 555-1234" },
    { type: "fax", number: "646 555-4567" }
  ]
}

 JSON Format

• The JSON format follows the rules of object literals in JS

  • Strings, numbers and booleans are valid JSON

  • Arrays  and objects are valid JSON

// Strings
"this is string and is valid JSON"

// Arrays
[5, 'string', true]

// Objects
{ 
  "firstname": "Doncho",
  "lastname": "Minkov",
  "occupation": "Technical Trainer"
}

Working with JSON

 JSON.NET Library

• JSON.NET is a library for parsing JSON in .NET

  • Has better performance than the JavaScriptSerializer

  • Provides LINQ-to-JSON

  • Has an out-of-the-box support for parsing between JSON and XML

// Serialize an object:
var jsonObj = JsonConvert.SerializeObject(obj);

// Deserialize an object:
var copy = JsonConvert.DeserializeObject<ObjType>(jsonObj);

 Configuring JSON.NET

• JSON.NET can be configured to:

  • Indent the output JSON string

  • To convert JSON to anonymous types

  • To control the casing and properties to parse

  • To skip errors

• JSON.NET also supports:

  • LINQ-to-JSON

  • Direct parse between XML and JSON

 Configuring JSON.NET

• To indent the output string use

  • Formatting.Indented

• Deserializing to anonymous types:

var json = @"{ 
   ""fname"": ""Doncho"",
   ""lname"": ""Minkov"",
   ""occupation"": ""Technical Trainer"" 
 }";

var template = new { FName  = "", LName = "", Occupation = "" };
var person = JsonConvert.DeserializeAnonymousType(json, template);

 JSON.NET Parsing Objects

• By default JSON.NET takes each Property/Field from the public interface of a class and parses it

• This can be controlled using attributes:

  • [JsonProperty] tells the parser that Username is called user in the JSON data

  • [JsonIgnore] tells the parser to skip the property Password

public class User
{
  [JsonProperty("user")]
  public string Username { get; set; }

  [JsonIgnore]
  public string Password { get; set; }
}

 JSON.NET Parsing Objects

• JSON.NET has a support for LINQ-to-JSON

var jsonObj = JObject.Parse(json);
Console.WriteLine("Places in {0}:", jsonObj["name"]);

jsonObj["places"]
    .Select(pl => string
        .Join(", ", pl["categories"].Select(cat => cat["name"]))))
    .Print();

 XML to JSON and JSON to XML

• Conversions from JSON to XML are done using two methods:

// XML to JSON
string jsonFromXml = JsonConvert.SerializeXNode(doc);

// JSON to XML
XDocument xmlFromJson = JsonConvert.DeserializeXNode(json);