Wilde

Project Information

• Project Name: 'Product X'
• Location: 'Bellaire'
• Company: Company projects
• Worker Names: 'Smith', 'Joyce'
• Worker Numbers: '123456789', '435435435'
• Last Hours: 20.0
• San First Hours: CZ2007

Introduction to Databases: Semi-Structured Data

• Professor: Cong Gao
• School: School of Computer Science and Engineering
• University: Nanyang Technological University, Singapore

Roadmap: Semi-Structured Data

• Topics:
  • Semi-structured Data
  • XML
  • XML DTD
  • JSON

The Value of Data

• The More Data, The Merrier:
  • Volume: GB -> TB -> PB
  • Variety: Data comes from everywhere in all shapes
  • Value: Often discovered later
• Power of Data:
  • The more services the merrier (10 -> 1000 -> 1M -> 1B)
• Goal: Platforms for data and services
• Services turn data into $$$
• Accessibility: Any data, any service, anywhere, and anytime

Data Sources and Types

• Data Sources:
  • Client Machines (Browser, Adobe Air, Adobe Flex, Mobile Games)
  • Servers of utility provider
• Communication: REST (http)
• Data Storage: DB
• Data Variety: Doc, Internal & External Data
• Network: Internet

Structured vs. Unstructured Data

• Relational Databases (Structured):
  • Data resides in tables.
  • Schema must be defined before data entry.
  • Every row conforms to the table schema.
  • Changing the schema is difficult and can break many things.
• Texts (Unstructured):
  • Data is free-form.
  • No schema, and it’s hard to define one.
  • Readers need to infer structures & meanings.
• Question: What’s in between these two extremes?

Semi-Structured Data

• Observation: Most data have "some" structure.
  • Examples:
    • Book: chapters, sections, titles, paragraphs, references, index.
    • Item for sale: name, picture, price, ratings, promotion.
    • Web page: HTML.
• Ideas:
  • Ensure data is "well-formatted."
  • If needed, ensure data is also "well-structured."
    • But make it easy to define and extend this structure.
  • Make data "self-describing."

A Brief History

• Database World:
  • 1970: Relational databases
  • 1990: Nested relational model and object-oriented databases
  • 1995: Semi-structured databases
• Documents World:
  • 1974: SGML (Structured Generalized Markup Language)
  • 1990: HTML (Hypertext Markup Language)
  • 1992: URL (Universal Resource Locator)
• Data + Documents = Information
  • 1996: XML (Extensible Markup Language)
  • URI (Universal Resource Identifier)

XML as Semi-Structured Data

• XML Definition: The EXtensible Markup Language
• Purpose: A flexible syntax for data: semi-structured data
• Use Cases:
  • Configuration files (e.g., Web.Config)
  • Replacement for binary formats (MS Word)
  • Document markup (e.g., XHTML)
  • Data exchange, semistructured data (sensor data, logs, blogs)
• Warning: Not normal form! Not even 1NF
• Popularity: XML is about half as popular as SQL

From HTML to XML

• HTML Example:
  • Displays a bibliography with two entries, including the titles, authors, and publication information.
• HTML - The HyperText Markup Language
• HTML describes the presentation

HTML Characteristics

• It’s mostly a “formatting” language
• It mixes presentation and content
• HTML - The HyperText Markup Language

XML Example

• XML Example:
  • Presents the same bibliographic information as the HTML example but focuses on the data content and structure, using tags to define elements like <title>, <author>, <publisher>, and <year>. This structure makes it easier to process and extract data.
• XML - The EXtensible Markup Language
• XML describes the content

XML Characteristics

• Text-based
• Capture data (content), not presentation
• Data self-describes its structure
  • Names and nesting of tags have meanings!
• XML - The EXtensible Markup Language

HTML vs. XML

• Difficulties with HTML:
  • Fixed set of tags
  • Elements have document structuring semantics
  • For presentation to human readers
  • Applications cannot consume and process HTML easily
• These difficulties are not in XML

XML Terminology

• Given the XML:

  <bibliography>
    <book ISBN="ISBN-10" price="80.00">
      <title>Foundations of Databases</title>
      <author>Abiteboul</author>
      <author>Hull</author>
      <author>Vianu</author>
      <publisher>Addison Wesley</publisher>
      <year>1995</year>
    </book>
  </bibliography>
  

• Terminology:

  • Tag names: book, title, …
  • Start tags: ,
  • End tags: , , …
  • An element is enclosed by a pair of start and end tags: …
  • Elements can be nested: ……
  • Empty elements: Can be abbreviated:
  • Elements can also have attributes:
  • Element Ordering generally matters, but not for attributes

Well-formed XML Documents

• A well-formed XML document:
  • Follows XML lexical conventions
    • Wrong: <section>We show that x < 0…</section>
    • Right: <section>We show that x &lt; 0…</section>
    • Other special entities: > becomes > and & becomes &
  • Contains a single root element
  • Has properly matched tags and properly nested elements
    • Right: <section>…<subsection>…</subsection>…</section>
    • Wrong: <section>…<subsection>…</section>…</subsection>

Tree Representation of XML Documents

• XML documents can be represented as trees, where elements are nodes, and nesting is represented through parent-child relationships.

XML Attributes Example

• Example:

  <book price = "55" currency = "USD">
    <title> Foundations of Databases </title>
    <author> Abiteboul </author>
    <year> 1995 </year>
  </book>
  

Attributes vs. Elements

• Using attributes and elements to represent data

  <book price = "55" currency = "USD">
    <title> Foundations of DBs </title>
    <author> Abiteboul </author>
    <year> 1995 </year>
  </book>
  
  <book>
    <title> Foundations of DBs </title>
    <author> Abiteboul </author>
    <year> 1995 </year>
    <price> 55 </price>
    <currency> USD </currency>
  </book>
  

• Attributes are alternative ways to represent data

Attribute Uniqueness

• Attribute names must be unique! (No Multisets)
• `<person name =