XML is a collection of standards for producing documents in such a way that they can be read by computers. It makes no mention of what the documents are for or how they will be used.
XML has become a common means to send data between computer systems, especially across networks, because tools to produce and read it are available in every programming language. Schema and DTD belong to the same markup language.
XML Schema vs DTD
The main difference between DTDs and XML Schemas is that XML Schemas use an XML-based syntax, whereas DTDs use a special syntax that dates back to SGML DTDs. The converse is true for XML Schema, which is verbose but also uses tags and XML, making the syntax of XML Schema less scary to XML authors. Although DTDs are frequently chastised for requiring users to learn new grammar, the syntax is extremely simple.
XML is used to describe and validate XML data’s structure and content. The components, properties, and data types are defined by an XML schema. A set of objects are supported by the schema element. It is similar to a database schema, which explains how the data in a database is organized.
A document type definition is the full form of DTD. A document type definition (DTD) is a set of markup declarations for an SGML-family markup language that defines a document type (SGML, XML, HTML). The valid building pieces of an XML document are defined by a DTD. It contains a list of validated components and attributes that describe the document structure.
Comparison Table Between XML Schema And DTD
| Parameters of Comparison | XML Schema | XML DTD |
| Definition | XML Schema helps in the generation of XML documents and defines rules of attributes and elements of an XML document. | DTD describes the attributes and structure of an XML document and languages. |
| Namespace | XML Schema supports namespace. | XML DTD doesn’t support namespace. |
| Structure Control | It gives better structure control of any XML document. | It gives less structure control of any XML document compared to Schema. |
| Extensible | XML Schema is extensible | XML DTD is not extensible |
| Data Types | The schema supports Data Types. | XML DTD doesn’t support Data Types. |
What is XML Schema?
XML Schemas are written in the XML language. Data types are supported by XML Schemas.
In XML Schema, there are two types: simple types and complex types. The main difference is that basic types cannot have attributes or variables. Complex types and child elements are examples of this.
The sequence in XML Schema allows you to specify the order in which things happen, which child items are required to show minimum Attribute
The term “occurs” refers to the number of times something happens maximum element in the Schema. The maximum value is specified by occurs; it can be adjusted to boundless. The default attributes are 1 for both minimum and maximum values.
Features of XML Schema:
The following are some of the notable features:
- Defining an XML file’s structure
- Putting restrictions on things like recurring pieces is a good illustration of this type.
- Specifying which data types are acceptable for specific elements.
- Defining static values and constraints for elements’ values.
- Define the order in which the child items should appear.
The easiest approach to ensure that all XML data you handle is well-formed and conforms to the structure you have to use an established schema to validate it.
What is DTD?
The XML Document Type Declaration, or DTD, is a mechanism to fully specify the XML language. DTDs validate an XML document’s structure and vocabulary by comparing it to the grammatical rules of the relevant XML language.
The following is an example of an XML document:
Well-formed: If the XML document follows all of the general XML criteria, such as properly nesting tags, balancing opening and closing tags, and ending empty tags, It is referred to as well-formed if it ends with ‘/>’. (or)
Valid: An XML document is considered to be valid if it is not just well-formed but also conforms to the specifications to a DTD that specifies which tags it uses, what characteristics those tags might include, and how it should be formatted among other properties, which tags can be found inside other tags.
Advantages of DTD Documentation:
- You can define your XML file format. A user/developer can grasp the data structure by looking at this document.
- Validation- It allows you to examine the authenticity of XML files by determining whether or not they are valid.
- The elements are in the correct sequence, the mandatory elements and attributes are in place, and the elements are in the correct order.
- There haven’t been any mistakes with elements or characteristics, and so on with DTD so far.
Disadvantages of adopting DTD
- The namespaces are not supported. A namespace is a technique that allows elements and data to be grouped.
- Groups can be given attribute names. In a DTD, however, namespaces must be specified.
- Namespaces are declared within the DTD, which defeats the purpose of utilizing them.
- Only the text string data type is supported.
Main Differences Between XML Schema And DTD
- XML Schemas are more powerful and richer than DTDs and can be extended in the future.
- XML Schemas are indicated with XML-based syntax whereas DTD is indicated with SGML syntax.
- XML schemas are not simple to learn and implement while DTDs are simple to learn and implement.
- The schema supports string data types, Boolean, and numeric on the other hand DTD doesn’t support these data types.
- XML schemas help in defining the order of child elements while XML DTD helps in defining the order of child elements.
Conclusion
XML is a handy format to store any kind of database. XML has gone beyond formats with Schemas and DTDs. The main difference between these two languages holds within the power they hold over a document.
XML Schemas lack many advantageous features that DTD possesses, the main feature is that it can define inline which is not present in XML schemas. This feature allows us to contain the small document as they are but the same features act as a disadvantage when it comes to large documents.
References
- https://dl.acm.org/doi/abs/10.1145/1017074.1017095
- http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.79.4962&rep=rep1&type=pdf