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    Definitions 6 min read

    Canonical is the term used to describe an entity that adheres to an original, authoritative text or to a set of rules, principles, and criteria. It has a broad range of usage in various fields, such as religious writings, medicine, mathematics, and computer science.

    How is the term canonical used?

    While what can be referred to as “canonical” is limitless, the term is commonly used in IT and technology settings.

    In computer science, canonicalization refers to the standard state or behavior of an attribute. It is conforming to an accepted rule or procedure. This term has been borrowed from mathematics, where it refers to concepts that are unique and/or natural. For example, the canonical way to organize a file system is as a hierarchy.

    In information technology (IT), the term refers to a standard state or convention of organizing data. It is a term used to distinguish the normalized data format generated from the non-standardized or non-canonical data. Also known as c14n, canonicalization is widely practiced in IT applications, like Unicode, XML, web servers, and search engine optimization (SEO).

    Conforming to standard rules not only simplifies tasks but also secures information. Data representations are compared to get the equivalence and organize their structures to improve calculations and procedural efficiencies. This is particularly useful for data modeling, file security, Unicode, SEO, IP address, and programming.

    Canonical vs. non-canonical

    If canonical refers to the established pathways and standard rules to follow that make data conversion more efficient, non-canonical are the processes or behaviors that do not conform to the canonical.

    Canonical quivalence in Unicode

    In natural language processing (NLP), there have to be some standard rules that the input characters must follow, otherwise, the text is unreadable. Completely different characters might appear identical when rendered, which could create confusion. Some characters, especially in many European languages, have diacritics with hidden code properties. They could affect the reading of NLP. 

    Canonicalization resolves the unreadability of a wide range of characters that come with different variants. Unicode, an international coding standard, normalizes the canonical equivalences of the characters by breaking them down into independent parts. It results in format standardization, assigning a numeric value to every character, digit, or symbol. It becomes easy for NLP to identify or read characters. 

    Filenames and pathnames

    Canonical has the same meaning and application in creating standards for a filename or location in the directory. A canonical filename is unique and absolute and is fundamental to computer security. Files are executed only with pathnames to their specific directory, which helps keep files secure.

    Whether in Java, UNIX, or Windows systems, multiple paths lead to issues linked to relative or non-canonical paths. Using getPath() or getAbsolutePath(), the created file object returns to the pathname argument. But with getCanonicalPath(), the pathname is converted into an absolute and unique form independent from the root directories, removing redundancies from the pathname, fixing symbolic links (in UNIX), and converting characters into a standardized format (in Windows). 

    Canonicalization in IP addresses and XML  

    An IP address, which is vital for a host computing device to connect to the Internet, might have aliases that need to be resolved. The canonical name (CNAME) in the DNS database points the computer’s domain name to the IP address, creates multiple aliases, and keeps a separate record of the aliases. A specific hostname, which is directed to the root domain, is assigned to each alias or network service.

    In a web server, canonical data obtains specific information and automatically interprets unknown user-defined labels. It identifies threats with precision, thereby limiting them.

    The physical representation of documents and subdocuments in XML vary in structure, encoding, and order attributes. Having canonical representations helps in identifying specific sets of nodes—element, attribute, and namespace. A standardized encoding of each string of characters avoids the threats and possibilities of bugs in the code.

    Standard XML resolves references in the namespace, removes spaces within tags, and cuts redundancies. It generates an exclusive canonical form of an XML document subset and repairs a malformed HTML, making it a valid XML. 

    Canonical Ltd.

    Canonical Ltd. is a UK-based, privately held computer software company founded by Mark Shuttleworth created to market commercial support and related services for Ubuntu and related projects.

    The canonical model

    A canonical data model stands independent from other applications and features a standard form of producing, receiving, and consuming messages. In a data exchange involving multiple participants, there must be a standard format. Having the same sets of data or similar information in different formats can be confusing to the machine. So the message is translated first into the canonical format, and then from canonical into other formats. It reduces complexity and helps businesses and enterprises speed up the delivery of information, products, or services.

    Canonicalization in SEO: Addressing content duplication

    In SEO, canonicalization functions to distinguish the URL of the original web content from other URLs that appear to have similar contents so that when the search engine bot (crawler) indexes the information, it avoids making duplicates.

    Web content with multiple URLs confuses the search engine bot that might show multiple results with the same content. With a canonical tag in place, search engines easily identify the web content to appear on queries or searches. It allows the search engine to pick the canonical URL, preventing it from showing confusing results.

    Canonical XML

    Canonical XML is a normal form of Extensible Markup Language (XML), which allows designers to create customized tags, enabling the definition, transmission, validation, and interpretation of data between applications and between organizations. Canonical XML is intended to allow relatively simple comparisons of pairs of XML documents for equivalence. It removes non-meaningful differences between the documents.

    Advantages of canonicalization

    1. Simplifies the otherwise complex procedures of establishing a common standard to follow among varying choices
    2. Creates stability in the flow (interchange) of data, particularly if the data format or message requires translation
    3. Provides a security layer to database management systems and minimizes threats to web servers