93

Since we can query on the XML file from C# (.NET), why do we need an XSD file? I know it is metadata file of particular XML file. We can specify the relationships in XSD, but what is its functioning then?

XML

<?xml version="1.0" encoding="utf-8" ?>
<Root>
  <Customers>
    <Customer CustomerID="GREAL">
      <CompanyName>Great Lakes Food Market</CompanyName>
      <ContactName>Howard Snyder</ContactName>
      <ContactTitle>Marketing Manager</ContactTitle>
      <Phone>(503) 555-7555</Phone>
      <FullAddress>
        <Address>2732 Baker Blvd.</Address>
        <City>Eugene</City>
        <Region>OR</Region>
        <PostalCode>97403</PostalCode>
        <Country>USA</Country>
      </FullAddress>
    </Customer>
  </Customers>
  <Orders>
    <Order>
      <CustomerID>GREAL</CustomerID>
      <EmployeeID>6</EmployeeID>
      <OrderDate>1997-05-06T00:00:00</OrderDate>
      <RequiredDate>1997-05-20T00:00:00</RequiredDate>
      <ShipInfo ShippedDate="1997-05-09T00:00:00">
        <ShipVia>2</ShipVia>
        <Freight>3.35</Freight>
        <ShipName>Great Lakes Food Market</ShipName>
        <ShipAddress>2732 Baker Blvd.</ShipAddress>
        <ShipCity>Eugene</ShipCity>
        <ShipRegion>OR</ShipRegion>
        <ShipPostalCode>97403</ShipPostalCode>
        <ShipCountry>USA</ShipCountry>
      </ShipInfo>
    </Order>
    <Order>
      <CustomerID>GREAL</CustomerID>
      <EmployeeID>8</EmployeeID>
      <OrderDate>1997-07-04T00:00:00</OrderDate>
      <RequiredDate>1997-08-01T00:00:00</RequiredDate>
      <ShipInfo ShippedDate="1997-07-14T00:00:00">
        <ShipVia>2</ShipVia>
        <Freight>4.42</Freight>
        <ShipName>Great Lakes Food Market</ShipName>
        <ShipAddress>2732 Baker Blvd.</ShipAddress>
        <ShipCity>Eugene</ShipCity>
        <ShipRegion>OR</ShipRegion>
        <ShipPostalCode>97403</ShipPostalCode>
        <ShipCountry>USA</ShipCountry>
      </ShipInfo>
    </Order>
  </Orders>
</Root>

I want to get data from the Order elements according to a provided CustomerID.

Also: What is the purpose of giving the relationships in XSD?

kjhughes
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Red Swan
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  • http://stackoverflow.com/questions/2333998/what-is-the-difference-between-xml-and-xsd, may also can be referred! – AVA Oct 13 '15 at 14:21

10 Answers10

114

XSD files are used to validate that XML files conform to a certain format.

In that respect they are similar to DTDs that existed before them.

The main difference between XSD and DTD is that XSD is written in XML and is considered easier to read and understand.

Jamie Counsell
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Oded
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  • thanks, so can i query on xsd files from c3.net using Linq for get the data from xml file? How? – Red Swan Aug 04 '10 at 08:04
  • @Lalit - Linq has nothing to do with it. – Oded Aug 04 '10 at 08:07
  • Another important difference is that you can't do lots of stuff easily done in XSD in a DTD. – mort Aug 04 '10 at 08:09
  • So for getting data, I can use only the xml file right? I have no need to generate its schema file. (I don't want to validate it for now) I just want to get data of xml that have various records dependent on IDs maps in each element. – Red Swan Aug 04 '10 at 08:14
  • @mort - there are also things you can do with DTDs that cannot be done in XSD. – Oded Aug 04 '10 at 08:16
  • @Oded - yes, but IMHO a lot of basic stuff is a real pain in DTD – mort Aug 04 '10 at 08:20
  • Ok thanks all, So waht is main purpose of setting the relationships in schema file then? why its need. – Red Swan Aug 04 '10 at 08:25
  • @mort - never said that wasn't the case... that's why you don't see DTDs as much anymore :) – Oded Aug 04 '10 at 08:27
  • @Lalit - If you _need_ to make sure that the relationships are correct, you can use an XSD to validate the XML, to make sure that it has the correct relationships. If you don't care about such things, you don't need XSD. – Oded Aug 04 '10 at 08:31
  • Ok that's means though I what to get data from xml file then no need to set relationships ? hmmmmmm... thanks – Red Swan Aug 04 '10 at 09:07
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    @Lalit - if you don't care about the relationships as such and don't need to check that they conform to some sort of rule (codified in an XSD), then don't use an XSD and just query the XML directly. – Oded Aug 04 '10 at 09:22
49

Without XML Schema (XSD file) an XML file is a relatively free set of elements and attributes. The XSD file defines which elements and attributes are permitted and in which order.

In general XML is a metalanguage. XSD files define specific languages within that metalanguage. For example, if your XSD file contains the definition of XHTML 1.0, then your XML file is required to fit XHTML 1.0 rather than some other format.

Ben Barden
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Oleg
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20

You mention C# in your question so it may help to think of as XSD as serving a similar role to a C# interface.

It defines what the XML should 'look like' in a similar way that an interface defines what a class should implement.

Garry
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    If you take a class and an interface it is supposed to implement, you can tell if the class is correct. In the same way, if you take an xml file and it's xsd, you can tell if the xml is correct. – Garry Aug 04 '10 at 09:39
17

XSDs constrain the vocabulary and structure of XML documents.

  • Without an XSD, an XML document need only follow the rules for being well-formed as given in the W3C XML Recommendation.
  • With an XSD, an XML document must adhere to additional constraints placed upon the names and values of its elements and attributes in order to be considered valid against the XSD per the W3C XML Schema Recommendation.

XML is all about agreement, and XSDs provide the means for structuring and communicating the agreement beyond the basic definition of XML itself.

Community
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kjhughes
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12

Also questions is: What is the purpose of giving the relationships in xsd.

Suppose you want to generate some XML for an external party's tool, or similar - how would you know what structure it is allowed to follow to be used correctly for their tool? you write to a schema. Likewise if you want other people to use your tool, you would write a schema for them to follow. It may also be useful for validating your own XML.

Robert
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9

Before understanding the XSD(XML Schema Definition) let me explain;

What is schema?

for example; emailID: peter#gmail

You can identify the above emailID is not valid because there is no @, .com or .net or .org.

We know the email schema it looks like peter@gmail.com.

Conclusion: Schema does not validate the data, It does the validation of structure.

XSD is actually one of the implementation of XML Schema. others we have

We use XSD to validate XML data.

Premraj
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7

An XSD is a formal contract that specifies how an XML document can be formed. It is often used to validate an XML document, or to generate code from.

troelskn
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5

The xsd file is the schema of the xml file - it defines which elements may occur and their restrictions (like amount, order, boundaries, relationships,...)

mort
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5

An XSD file is an XML Schema Definition and it is used to provide a standard method of checking that a given XML document conforms to what you expect.

a'r
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5

An .xsd file is called an XML schema. Via an XML schema, we may require a certain structure in a given XML - which elements in which order, how many times, with which attributes, how they are nested, etc. If we have a schema for our XML input, we can verify that it contains the data we need it to contain, and nothing else, with a few lines invoking a schema validator.