SMILA/Documentation/Web Crawler

What does Web Crawler do

A WebCrawler collects data from the internet. Starting with an initial URL it recursively crawls all linked Websites. Due to the manifold capabilities of webpage structures and much linking to other pages, the configuration of this crawler enables you to limit the downloaded data to match your needs.

Crawling configuration

Defining Schema: org.eclipse.smila.connectivitiy.framework.crawler.web/schemas/WebIndexOrder.xsd

Crawling configuration explanation

The root element of crawling configuration is IndexOrderConfiguration and contains the following sub elements:

• DataSourceID – the identification of a data source.
• SchemaID – specify the schema for a crawler job.
• DataConnectionID – describes which agent crawler should be used.
  • Crawler – implementation class of a Crawler.
  • Agent – implementation class of an Agent.
• CompoundHandling – specify if packed data (like a zip containing files) should be unpack and files within should be crawled (YES or NO).
• Attributes – list all attributes which describe a website.
  • FieldAttribute (URL, Title, Content):
    • Type (required) – the data type (String, Integer or Date).
    • Name (required) – attributes name.
    • HashAttribute – specify if a hash should be created (true or false).
    • KeyAttribute – creates a key for this object, for example for record id (true or false).
    • Attachment – specify if the attribute return the data as attachment of record.
  • MetaAttribute (MetaData, ResponseHeader, MetaDataWithResponseGeaderFallBack, MimeType):
    • Type (required) – the data type (String)
    • Name (required) – attributes name
    • Attachment - specify if the attribute return the data as attachment of record.
      • ReturnType – structure the metadata will be returned
        • MetaDataString – default structure, metadata is returned as single string, for example:

<A n="ResponseHeaser">
  <L>
    <V>Content-type: text/html</V>
  </L>
  ...
</A>

• MetaDataValue – only values of metadata are returned, for example:

<A n="ResponseHeader">
  <L>
    <V>text/html</V>
  <L>
</A>

• MetaDataMObject – metadata is returned as MObject containing attributes with metadata names and values, for example:

<A n="ResponseHeader">
  <O>
    <A n="Content-Type">
      <L>
        <V>text/html</V>
      </L>
    </A>
    ...
  </O>
</A>

• Process – this element is responsible for selecting data
  • Website - contains all important information for accessing and crawling a website.
    • ProjectName - defines project name
    • Sitemaps - for supporting Google site maps. sitemap.xml, sitemap.xml.gz and sitemap.gz formats are supported. Links extracted from <loc> tags are added to the current level links. Crawler looks for the sitemap file at the root directory of the web server and then caches it for the particular host.
    • Header - request headers separated by semicolon. Headers should be in format "<header_name>:<header_content>", separated by semicolon.
    • Referer - to include "Referer: URL" header in http request.
    • EnableCookies - enable or disable cookies for crawling process (true or false)
    • UserAgent - element used to identify crawler to the server as a specific user agent origination the request. The UserAgent string generated looks like the following: Name/Version (Description, Url, Email)
      • Name (required)
      • Version
      • Description
      • URL
      • Email
    • Robotstxt element used for supporting robots.txt information. The so-named Robots Exclusion Standard tells crawler how to crawl a website – or rather which resources should not be crawled. See [[1]]
      • Policy: there are five types of policies offered on how to deal with robots.txt rules:
        1. Classic. Simply obey the robots.txt rules. Recommended unless you have special permission to collect a site more aggressively.
        2. Ignore. Completely ignore robots.txt rules.
        3. Custom. Obey your own, custom, robots.txt instead of those discovered on the relevant site. The attribute Value must contain the path to a locally available robots.txt file in this case.
        4. Set. Limit robots names which rules are followed to the given set. Value attribute must handle robots names separated by semicolon in this case.
      • Value: specifies the filename with the robots.txt rules for Custom policy and set of agent names for the Set policy.
      • AgentNames: specifies the list of agents we advertise. This list should be started with the same name as UserAgent Name (for example: crawler user-agent name that is used for the crawl job)
    • CrawlingModel: there are two models available:
      • Type: the model type (MaxBreadth or MaxDepth)
      1. MaxBreadth: crawling a web site through a limited number of links.
      2. MaxDepth: crawling a web site with specifying the maximum crawling depth.
      • Value: parameter (Integer)

See also

• Crawler
• Filesystem Crawler
• JDBC Crawler