Learning about the basic constructs of XML

A few weeks ago I wrote about relational data models and databases and some of the basic principles which I learned about in an online Stanford course. As part of the same course I recently learned about “XML” which stands for Extensible Markup Language, a standard for data representation and exchange. Having worked in the entertainment industry for a few years now, I’ve often find myself looking at metadata in the form of XML, but it was great to get a good refresher as part of my course.

These are some of the basic constructs of XML:

  • Tagged elements (nested) – an opening and a closing tag
  • Attributes – attributes tend to consist of: a name (unique), an equal sign (=) and an attribute value
  • Text – also known as “character data”, this can be as simple as “Marc Abraham” or “123456”

The instructor, Jennifer Widom, then went on to explain the differences between the relational data model and XML:

Relational data (eg. SQL):

  1. Structure: Tables
  2. Schema: Fixed in advance
  3. Queries: Simple, nice language
  4. Ordering: None, unordered
  5. Implementation: Native


  1. Structure: Hierarchical tree, graph
  2. Schema: Flexible, “self-describing”
  3. Queries: Less simple, more complex
  4. Order: Implied ordering
  5. Implementation: Add-on

With XML, validation is a key aspect. In an oversimplified way, it comes down to taking an XML document and validate it against a set “XSD” (XML Schema Descriptor). This process determines whether the XML document is valid or invalid (see Fig. 1 below). During the class, Jennifer also highlighted that XML documents contain two file types. First, a schema file which contains the XSD. Second, the actual data file.

I then struggled a bit when Jennifer talked about “DTDs”. I subsequently learned that “DTD” stands for ‘Document Type Definition’ and is a set of markup declarations which defines the legal building blocks of an XML document.

There are four features of an XML schema which aren’t present in DTDs:

  • Key declarations – In DTDs, document or item IDs have to be globally unique. An XML ID can be specified through an attribute value only. This means that you can’t index elements in the XML based on a parent-child relationship (see Fig. 2 below). Key declarations in XML aim to overcome such limitations.
  • Type values  XML Schema has a lot of built-in data types. The most common types are string, decimal, integer, boolean, date and time. I’ve found some useful examples of ‘simple type’ and ‘complex types’ XML schema (see Fig. 3 below).
  • References – References can refer to already defined keys (see my previous point about key declarations) or so-called “typed pointers”. A typed pointer must point to a specific element of the XML (e.g. a string) which in term must confirm to the specification as laid out in the pointer.
  • Currents constraints  In XML one can specify how many times an element type is allowed to occur. One can thus specify a minimum and a maximum number of occurrences.

Main learning point: In her online video on the basics of XML, Jennifer Widom provided a useful overview of XML. Even though I had looked at XML schema before, it was good to understand more about some of the foundations behind XML and XML validation.

Fig. 1 – Sample XML validator – Taken from: http://www.deitel.com/articles/xml_tutorials/20060401/XMLStructuringData/XMLStructuringData_Page4.html



Fig. 2 – Sample XML, highlighting XML ID requirement – Taken from: http://msdn.microsoft.com/en-us/library/aa302297.aspx

<?xml version="1.0"?>
<!DOCTYPE orders [
  <!ELEMENT order ANY>  
  <!ATTLIST order
    orderno ID #REQUIRED   
  <order orderno="id10952" date="4/15/96" shipAddress="Obere Str. 57"/>
  <order orderno="id10535" date="6/13/95" shipAddress="Mataderos  2312"/>


Fig. 3 – Examples of simple type and complex type XML schema – Taken from: http://www.xmlmaster.org/en/article/d01/c05/

Simple Type Example

<xs:element name=”Department” type=”xs:string” />

Here, the section described together with “xs:string” is an embedded simple type according to XML Schema. In this example, we have established the definition that the data type for the element called “Department” is a text string.

Complex Type Example

<xs:complexType name=”EmployeeType”>
<xs:sequence maxOccurs=”unbounded”>
<xs:element ref=”Name” />
<xs:element ref=”Department” />
<xs:element name=”Name” type=”xs:string” />
<xs:element name=”Department” type=”xs:string” />

In this case the type name “EmployeeType” is designated by the name attribute of the complexType element. A model group (what designates the order of occurrence for the child element) is designated in the child element.

New types are created by placing restrictions on or extending simple or complex types. In this volume, we will discuss restrictions and extensions for simple types.

Related links for further learning:

  1. http://www.rpbourret.com/xml/XMLAndDatabases.htm
  2. http://stackoverflow.com/questions/966901/modeling-xml-vs-relational-database
  3. http://www-01.ibm.com/support/knowledgecenter/SSEPGG_9.1.0/com.ibm.db2.udb.apdv.embed.doc/doc/c0023811.htm
  4. http://www.deitel.com/articles/xml_tutorials/20060401/XMLStructuringData/XMLStructuringData_Page4.html
  5. http://en.wikipedia.org/wiki/Document_type_definition
  6. http://www.w3.org/TR/xmlschema-1/
  7. http://msdn.microsoft.com/en-us/library/aa302297.aspx
  8. http://www.w3schools.com/schema/schema_simple.asp
  9. http://www.xmlmaster.org/en/article/d01/c05/
  10. http://www.w3.org/TR/xptr-framework/
  11. http://www.xmlnews.org/docs/xml-basics.html



UX features for online retailers to consider

I just read a really insightful piece by Paul Bryan on 10 Absentee UX Features on Top e-Commerce Sites. His agency, Usography, has conducted a Retailer UX audit, looking at the 100 top retail websites. The audit highlighted some key user experience (UX) features for brands to consider. From the 10 features that Bryan listed in his article, I particularly liked following UX features and looked for interesting examples to serve as good illustrations:

  1. Product videos – A case can be made for video as a good way of bringing a product to life, think clothes, shoes or cars. Good examples are Zappos and Mercedes Benz
  2. Combination of online and offline – Personally I’m all for the convenience of online shopping (and not having to go to a store). However, buy online-pick up in-store functionality offered by the likes of Tesco is rapidly gaining popularity
  3. Price drop alertsAmazon is a good example of a site that lets customers know when the price of a product they’ve indicated an interest in has dropped. It’s an incentive for customers to return the site and to buy the product.
  4. Customer product tagging – I think Bryan has a point when he states Letting customers create their own tags for products keeps the taxonomy fresh and relevant. However, call me a cynic, but I’m still not convinced most consumers would go through the effort of for example tagging a pair of red socks at Urban Outfitters.
  5. Co-shopping – This is a feature that lets customers in different locations view the same product and have a chat about it in a sidebar. Good examples are shopwithyourfriends.com and Dell.
  6. Virtual try-on – When talking about engaging customers, enabling them to virtually try on a product is a compelling feature. There are good examples in sites that let users try on glasses or see what they look like in clothes of their choosing.

Main learning point: even though eCommerce has been around for a while now there is a good number of exciting new UX features for retailers to implement. The research conducted by Usography shows that particularly social media oriented features such as customer tagging and co-shopping are on the rise and could help eCommerce sites to engage effectively with their target audience.

Related links for further learning:



http://www.usography.com/audit/ http://www.zugara.com/augmented-reality/e-commerce

What is HTML5 all about?

Last night I suddenly realised that I didn’t really know what “HTML5” was. I wasn’t devastated about it but I did feel it would be a good reason to learn a thing or two about HTML and HTML5.

The story starts with Tim Berners-Lee inventing the World Wide Web in the early 1990s and subsequently founding W3C, an organisation aimed at creating and maintaining uniform web standards. W3C launched the first version of HTML, followed by subsequent iterations, with HTML5 being the latest exponent.

HTML is essentially the mark-up language used for building and structuring web pages. The main things that the new HTML5 incorporates are features like video playback and drag-and-drop. Most of these features were previously dependent on 3rd party browsers such as Adobe Flash.

However, HTML doesn’t work in isolation: HTML, JavaScript and CSS are the three main components that make up a website. I’m not a developer but the way I understand it, you start by by creating your web pages using HTML (creating page structure and elements), then you apply JavaScript code to add interactivity and intelligence to the pages and, finally, you apply CSS to style the pages and to make them look good.

So this is what I’ve learnt about HTML and HTML5 so far:

  1. HTML is the standard mark-up language used by developers to build and structure web pages.
  2. If you were to compare a website to a house, then HTML acts as the foundation, JavaScript as the bricks and CSS as the paint
  3. What makes HTML5 different? It intends to facilitate the way in which we’re increasingly using the web; HTML5 supports video, audio and other rich applications that we’re previously dependent on 3rd party browsers.

Main learning point: as a non-technical head I like to try to keep technical things as simple as possible: HTML is the universal language used to build and structure web pages. HTML5 is its latest incarnation, currently ‘under construction’, which supports rich web applications and plug-ins.

Related links for further learning: