science

XML database

XML database is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand XML database rather than just read about it. In short: An XML database is a data persistence software system that allows data to be specified, and stored, in XML format. This data can be queried, transformed, exported and returned to a calling system.

Key takeaways

XML database belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect XML database to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of XML database from memory before moving on to harder problems.

Reference excerpt

An XML database is a data persistence software system that allows data to be specified, and stored, in XML format. This data can be queried, transformed, exported and returned to a calling system. XML databases are a flavor of document-oriented databases which are in turn a category of database.

Rationale for XML as a database format Reasons to store data in XML format as an XML database include:

An enterprise may have numerous XML documents with similar data, but dispersed in different XML formats. Conglomerating this data into a singular, standardized XML database structure will avoid compatibility issues Data may need to be exposed or ingested as XML, so using another format such as relational forces double-modeling of the data XML is very well suited to parse data, deeply nested data and mixed content (such as text with embedded markup tags) XML is human readable whereas relational tables require expertise to access Metadata is often available as XML Semantic web data is available as RDF/XML Provides a solution for Object-relational impedance mismatch Compatibility with XML use on the data transport layer

XML-enabled databases XML-enabled databases typically offer one or more of the following approaches to storing XML within the traditional relational structure:

XML is stored into a CLOB (Character large object) XML is "shredded" into a series of tables based on a schema XML is stored into a native XML Type as defined by ISO Standard 9075-14 RDBMS that support the ISO XML Type are:

IBM DB2 (pureXML) Microsoft SQL Server Oracle Database PostgreSQL Typically an XML-enabled database is best suited where the majority of data are non-XML. For datasets where the majority of data are XML, a native XML database is better suited.

Example of XML Type Query in IBM DB2 SQL

Native XML databases Native XML databases are especially tailored for working with XML data. As managing XML as large strings would be inefficient, and due to the hierarchical nature of XML, custom optimized data structures are used for storage and querying. This usually increases performance both in terms of read-only queries and updates. XML nodes and documents are the fundamental unit of (logical) storage, just as a relational database has fields and rows. One important caveat to this is that native XML databases need more disk space to store both data and indexes than XML-enabled databases do. As the size of the native XML database grows, the storage needs grow almost exponentially. The standard for querying XML data per W3C recommendation is XQuery; the latest version is XQuery 3.1. XQuery includes XPath as a sub-language and XML itself is a valid sub-syntax of XQuery. In addition to XPath, some XML databases support XSLT as a method of transforming documents or query results retrieved from the database.

Language features

Supported APIs

References

Worked examples

Example 1 — a first encounter with XML database

Start with the simplest possible case. Write down what XML database claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to XML database before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about XML database ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of XML database

In research: XML database appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses XML database in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: XML database is common in secondary-school and first-year university syllabi. It links to neighbouring topics Data management, Data modeling, Database management systems, so understanding it makes those chapters shorter.
In everyday life: Look for XML database outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study XML database in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what XML database means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain XML database out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is XML database in simple terms?

An XML database is a data persistence software system that allows data to be specified, and stored, in XML format. This data can be queried, transformed, exported and returned to a calling system.

Why does XML database matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study XML database?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on XML database.