2. AGENDA
What is scraping
Why we scrape
Where it is used
More on XPATH and RDF
Levels of scraping
1. Scraping service level
2. Syntactic level
3. Semantic level
Case study
Tools
Best practices
Challenges
4. More..
Any program that retrieves structured data from the web, and then
transforms it to conform with a different structure.
Isn’t that just ETL? (extract, transform, load), or cant we regex.
Nope. because ETL implies that there are rules and expectations, and
these two things don’t exist in the world of web data. They can change
the structure of their dataset without telling you, or even take the
dataset down.
5. Why Scraping?
Data is usually not in format we expect.
Get what you are interested in.
Web pages contain wealth of information (text form), designed mostly
for human Consumption
Interfacing with 3rd party that have no API access
Websites are more accurate than API’s
No IP rate limiting
Anonymous access
6. Where it is used
Developers use it to interface API
Mining Web content
Online adverts
RSS readers
Web browsers
7. Related terms
XML : A markup language that defines a set of rules for encoding
documents in a format that is both human and machine readable
RSS : RSS feeds enable web publishers provide summary/update of data
automatically. It can be used for receiving timely updates from news or blog
websites.
RDF :The Resource Description Framework (RDF) is a W3C standard for
describing Web resources, such as the title, author, modification date,
content, and copyright information of a Web page.
XPATH :is a query language used to navigate through elements and
attributes in an XML document.
8. More on Resource Description Framework
• RDF is a framework for describing resources on the web.
• RDF is designed to be read and understood by computers
• Similar to entity relationship model.
• RDF is written in XML.
• RDF is based upon the idea of making statements about resources (in
particular web resources) in the form of subject-predicate-object
expressions.
• The notion "The sky has the color blue" in RDF is as the triple:
a subject denoting "the sky", a predicate denoting "has the color",
and an object denoting "blue”
• A collection of RDF statements intrinsically represents a labeled,
directed multi-graph
9. The objects are:
• "Eric Miller"(predicate : "whose
name is"),
• em@w3.org (predicate "whose email
address is"),
• "Dr." (predicate : "whose title is").
The subject is a URI.
The predicates also have URIs. For
example, the URI for each predicate:
• "whose name is"
is http://www.w3.org/2000/10/swap
/pim/contact#fullName,
• "whose email address is"
is http://www.w3.org/2000/10/swap
/pim/contact#mailbox,
• "whose title is"
is http://www.w3.org/2000/10/swap
/pim/contact#personalTitle.
10. More on XPATH
• XPATH uses path expressions to select nodes or node-sets in an XML
document.
• XPATH includes over 100 built-in functions. There are functions for
string values, numeric values, date manipulation and time comparison,
node and Name manipulation, sequence, Boolean values, and more.
<?xml version="1.0" encoding="ISO-8859-1"?>
<bookstore>
<book>
<title lang="en">Harry Potter</title>
<author>J K. Rowling</author>
</book>
</bookstore>
<bookstore> (root element node)
<author>J K. Rowling</author> (element node)
lang="en" (attribute node)
J K. Rowling (atomic value)
11. <bookstore>
<book category="COOKING">
<title lang="en">Italian</title>
<author>Giada </author>
<year>2005</year>
<price>30.00</price>
</book>
• Select all the titles
“/bookstore/book/title”
• Select price nodes with price>35
“/bookstore/book[price>35]/price”
<book category="CHILDREN">
• Select the title of the first book
<title lang="en">Harry Potter</title>
“/bookstore/book[1]/title”
<author>J K. Rowling</author>
<year>2005</year>
<price>29.99</price>
</book>
</bookstore>
13. #1 : Syntactic scraping level.
This level gives support to the interpretation to the semantic scraping
model. It defines the required technologies to extract data from web
resources. Wrapping and Extraction techniques such as DOM selectors
are defined at this level for their use by the semantic scraping level.
14. Techniques in syntactic level
Content Style Sheet selectors.
XPATH selectors.
URI patterns.
Visual selectors.
15. Syntactic cont..
Selectors at the syntactic scraping level allow to identify HTML nodes.
Either a generic element or an identified element can be selected
using these techniques. Their semantics are defined in the next
scraping level, allowing to map data in HTML fragments to RDF
resources.
16. #2 : Semantic scraping level.
This level defines a model that maps HTML fragments to semantic
web resources. By using this model to define the mapping of a set of
web resources, the data from the web is made available as
knowledge base to scraping services.
• Apply the model to the definition of extractors of web resources.
• The proposed vocabulary serves as link between HTML document’s
data and RDF data by defining a model for scraping agents. With this
RDF model, it is possible to build an RDF graph of HTML nodes given
an HTML document, and connects the top and lowest levels in the
scraping framework to the semantic scraping level.
18. #3 : Scraping service level.
This level comprises services that make use of semantic data
extracted from un annotated web resources. Possible services that
benefit from using this kind of data can be opinion miners,
recommenders, mashups that index and filter pieces of news, etc.
Scraping technologies allow getting wider access to data from
the web for these kinds of services.
20. Case study
Scenario : has the goal of showing the most commented sports news
on a map, according to the place they were taken.
21. Challenges :
• The lack of semantic annotations in the sports news web sites,
• The potential semantic mismatch among these sites
• The potential structural mismatch among sites.
• Sites does not provide microformats, and do not include some
relevant information in their RSS feeds, such as location, users’
comments or ratings
Approach :
• Defining the data schema to be extracted from selected sports news
web sites,
• Defining and implementing these Extractors/Scrapers.
Recursive access is needed for some resources. For instance, a piece of
news may show up as a title and a brief summary in a newspaper’s
homepage, but offers the whole content (including location, authors,
and more) in its own URL.
• Defining the mashup by specifying the sources
30. Challenges
External sites can change without warning.
Figuring out the frequency is difficult, and changes can break scrapers easily
Bad HTTP status codes
Cookie check, Check referrer
Messy HTML markup
Data Piracy
31. Conclusion
• With plain text, we give ourselves the ability to manipulate knowledge,
both manually and programmatically, using virtually every tool at our
disposal.
• The problem behind web information extraction and screen scraping has
been outlined, while the main approaches to it have been summarized.
The lack of an integrated framework for scraping data from the web has
been identified as a problem, and presents a framework that tries to fill
this gap.
• Developer can have an API for each and every websites.
32. References
A SEMANTIC SCRAPING MODEL FOR WEB RESOURCES
By Jose´ Ignacio Ferna´ndez-Villamor, Jacobo Blasco-Garc´ıa, Carlos A´ . Iglesias, Garijo