Technatic | When you want to create a website, a developer must go through a coding and programming process, both of which require him to understand programming languages. Please remember, programming languages themselves have different rules and syntax, so the use of the elements cannot be mixed up.
For example, the coding rules for the HTML programming language will certainly be different from PHP or JavaScript. Not only are the rules different, the mechanism for using them is also not the same. In HTML itself, there are mechanisms that must be implemented to ensure that the coding structure is appropriate. This mechanism is carried out using a Document Type Definition.
What is Document Type Definition
However, what is meant by document type definition? In simple terms, DTD is a declaration that explains the structure of a document or data and is usually placed at the beginning of the document. In other words, DTD means the code placed at the beginning of a document to declare the type of document.
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It is known that this DTD contains declarations that explain the elements, attributes and entities of various types of documents. Generally, this document type definition is used to explain the document structure of the group:
- SGML
- GML
- HTML
- XML.
According to IBM, an XML document will be said to be valid if it is accompanied by a Document Type Definition in it. This also applies in HTML. Every HTML document must begin with a doctype declaration written with the code <!DOCTYPE>. The function of the HTML doctype is to tell the browser what type of document to use.
By knowing the HTML doctype, it will be easier for the browser to understand the type of document used, so it can display it on the website page. In practice, writing an HTML doctype declaration is not the same. In HTML4, document type declarations must be written to include a Uniform Resource Identifier (URI) that designates the location of the DTD document.
Benefits of DTD
From the previous explanation, it can be seen that the function of the DTD is to declare the type of document used so that it is easier for the browser to recognize. On the other hand, doctypes are also useful for helping developers ensure data conformity with applicable rules or syntax.
In fact, apart from DTD, there are now many alternative data schemas that developers can use to declare the type of a document. However, you also need to understand the document type definition because this scheme has many benefits. The benefits of DTD are as follows:
1. Data Validation
In line with its function, the first benefit of DTD is to help developers validate the data in the documents used. In this case, doctype will check the document structure to ensure there are no errors and inconsistencies. In other words, the benefit of DTD is to help validate data to maintain the quality and integrity of the data used.
2. Documentation
Document type definition acts as documentation that contains information about the structure and content format of an XML or HTML document. This documentation can be used as a guide for developers or programmers in the process of creating documents.
Apart from that, the document type definition can also be used as a contract that explains the terms and conditions of XML or HTML data.
3. Interoperability
The next benefit of document type definition is that it helps simplify the integration of data from different systems. Document type definition defines standard rules for exchanging data in XML documents, thereby encouraging system interoperability. Interoperability itself is the ability of applications or systems to exchange data and use information.
Types of DTD
In practice, writing document type definitions is divided into two types, namely internal and external. These two types certainly have different syntax. The following is the explanation.
1. Internal
XML and HTML documents can use internal document type definitions. It is said to be an internal DTD because the writing elements are included directly in the document.
Usually, the internal document type definition is written with the DOCTYPE keyword and placed at the beginning of the document before the opening tag. It is known that this type of document type definition is suitable for simple documents.
2. External
In contrast to the previous one, external DTDs declare document types via separate files. Writing this external doctype includes a link or file name that refers to an XML or HTML document. The doctype attribute used is SYSTEM or PUBLIC.
Unlike internal doctypes, external document type definitions are more suitable for more complex documents.
DTD Syntax
DTD syntax is the rules for writing a doctype so that it is structured and can explain the type of document. The document type definition syntax itself has several components which include elements, attributes and entities of data. The explanation of each DTD component is as follows.
1. Elements
In the document type definition, element declaration refers to the outline of a data. Usually, this element is written using the element keyword from the doctype.
Then, the keyword will be followed by the name element and content model or category, which can be EMPTY, ANY, PCDATA, or others. For more details, you can see the following syntax:
<!ELEMENT element-name category>
An example of writing an ANY category element in a DTD is as follows:
<!ELEMENT note ANY>
2. Attributes
The function of attributes in DTD is to provide further information regarding the characteristics of an element's properties.
Usually, this attribute component is written using the ATTLIST keyword followed by the element name, attribute name, attribute type, and value. More specifically, the rules for writing DTD attributes are as follows:
<!ATTLIST element-name attribute-name attribute type attribute-value>
3. Entity
Entities are written to define special characters in a DTD. The entity writing in DTD is as follows:
Internal: <!ENTITY entity-name “entity value”>
External: <!ENTITY entity-name SYSTEM “URI/URL”>
Conclusion
In conclusion, DTD is a declaration that explains the data structure and format of a document, be it XML or HTML. Document type definition is important in the website creation process because every XML or HTML document must be accompanied by this declaration. With a document type definition, it is easier for the browser to recognize the type of data used, so it can display it on the website.
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Furthermore, document type definition can also help developers to maintain coding consistency and quality according to predetermined standards. Therefore, don't forget the document type definition when you want to create a website, okay? Unfortunately, creating a document type definition for XML or HTML may be difficult for laypeople or beginners.