Based on XSD: http://www.w3schools.com/Schema/default.asp

* example:

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="note">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="to" type="xs:string"/>
                <xs:element name="from" type="xs:string"/>
                <xs:element name="heading" type="xs:string"/>
                <xs:element name="body" type="xs:string"/>
           </xs:sequence>
        </xs:complexType>
    </xs:element>
</xs:schema>

* elementFormDefault="qualified" indicates that all elements in the XML must be namespace qualified

* to reference an XSD in an XML document the main node has to have the following attributes:

• xmlns="http://www.w3schools.com" - default namespace declaration
• xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" - make XML Schema Instance namespace available
• xsi:schemaLocation="http://www.w3schools.com location_of_your_schema.xsd" - location of the schema to be used with given namespace

Elements in XSD schema:

• simple element (e.g. <xs:element name="to" type="xs:string"/> ) - can contain only text (i.e. boolean, string, date, etc.), you can also restrict its type; the most common types:
  - xs:string
  - xs:decimal
  - xs:integer
  - xs:boolean
  - xs:date
  - xs:time
  * you can also specify a default value for an element;
• an attribute - is a simple element (e.g. <xs:attribute name="xxx" type="yyy"/> ) - you can specify a default or a fixed (cannot be changed) value of an attribute; to make an attribute required you have to specify it, by using use="required" attribute;
• complex element - composed of other elements and/or text; can also contain empty elements; there are two ways of defining a complex type:
  

  <xs:element name="employee"> <xs:complexType>  <xs:sequence>  <xs:element name="firstname" type="xs:string"/>  <xs:element name="lastname" type="xs:string"/>  </xs:sequence> </xs:complexType> </xs:element>

  <xs:element name="employee" type="personinfo"/> <xs:complexType name="personinfo"> <xs:sequence>  <xs:element name="firstname" type="xs:string"/>  <xs:element name="lastname" type="xs:string"/> </xs:sequence> </xs:complexType>

  In case of second solution, several elements can refer to the same complex type, moreover, new complex types can be built on top of existing ones, in the following way:
  

  <xs:complexType name="fullpersoninfo">
  <xs:complexContent>
    <xs:extension base="personinfo">
      <xs:sequence>
      ... new elements ...
      </xs:sequence>
    </xs:extension>
  </xs:complexContent>
  </xs:complexType>

• empty element (i.e. with even no text inside):
  

  <xs:element name="product">
    <xs:complexType>
    </xs:complexType>
  </xs:element>

  * there are special ways to define a complex element: with text only, with other elements only, with both text and other elements - i nie widze w tym zadnej logiki; for more information on this see: http://www.w3schools.com/Schema/schema_complex_elements.asp

Facets (restrictions):

• restrictions on simple types:
  

  <xs:element name="car">
  <xs:simpleType>
    <xs:restriction base="xs:string">
    <xs:restriction_type value="..."/>
    ...
    <xs:restriction>
  </xs:simpleType>
  </xs:element>

  (more here: http://www.w3schools.com/Schema/schema_facets.asp)

Indicators:

1. elements after "<xs:complexType>:
   * All - kazde dziecko musi sie pojawic przynajmniej raz, w dowolnej kolejnosci;
   * Choice - jedno z dzieci ma sie pojawic;
   * Sequence - wszystkie dzieci w podanej kolejnosci
2. attributes in element's definition:
   * maxOccurs
   * minOccurs
   * "For all "Order" and "Group" indicators (any, all, choice, sequence, group name, and group reference) the default value for maxOccurs and minOccurs is 1"
   * you can use maxOccurs="unbounded" to have the element appearing unlimited number of times
3. element groups and attribute groups (can be used among other elements/attributes):
   - this is a reference to groups of elements: <xs:group ref="persongroup"/>
   - and this is a reference to a group of attributes:

   <xs:element name="person">
   <xs:complexType>
     <xs:attributeGroup ref="personattrgroup"/>
   </xs:complexType>
   </xs:element>

   read more here: http://www.w3schools.com/Schema/schema_complex_indicators.asp

Other elements:

• "any" element: <xs:any minOccurs="0"/>
• "anyAttribute" element: <xs:anyAttribute/>
• what is interesting, with usage of the two above we can create extensible documents; also we can make a document can use e.g. two schemas, one for main part, and another for subparts

Element substitution:

• <xs:element name="name" type="xs:string">
  <xs:element name="navn" substitutiongroup="name">

  - now "navn" can be used instead of "name"; we can also block an element from others substituting it, by using: block="substitution" attribute within the original element; read more here: http://www.w3schools.com/Schema/schema_complex_subst.asp

Dividing and organizing the schema: http://www.w3schools.com/Schema/schema_example.asp (this is quite important...)

More about data types - read here: http://www.w3schools.com/Schema/schema_dtypes_string.asp

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