| What is it? | |
| Who is to blame? | |
| Why/where is it? | |
| When will it be visible? |
| �Pages� (text, images, other files, other info) accessible over the Internet with a Web browser that search engines do not include in their indexes, because either | ||
| they are technically inaccessible, or | ||
| they are excluded by choice. | ||
| No one and everyone: | ||
| Directories don�t care about completeness | ||
| Indexes can�t keep up with growth of pages | ||
| Webmasters may not welcome spiders | ||
| We don�t want to pay for information | ||
| Pages are ordinary, but inaccessible. | ||
| �In the context of the Bow Tie Theory they are �disconnected.� | ||
| Hence spiders/crawlers cannot find them. | ||
| Pages are ordinary, but excluded by | ||
| Webmaster:� Robots Exclusion Protocol, | ||
| which is implemented by including a file such as www.mysite.com/robots.txt, containing | ||
| User-agent:� * | ||
| Disallow:� / | ||
| Pages are ordinary, but excluded by | ||
| Webmaster:� Robots Exclusion Protocol | ||
| Webmaster:� Robots META tag, which is implemented by putting a line like this in the <head> section of the HTML code: | ||
| <meta name=�robots" content=�noindex, nofollow"> | ||
| Pages are ordinary, but excluded by | |||
| Robots Exclusion Protocol or META tag, because | |||
| Content changes frequently | |||
| Extra load on server | |||
| Older content is archived/pay-only | |||
| Search engine: | |||
| some content is �unworthy� | |||
| some content is too deep | |||
| Pages are ordinary*, but incomprehensible | ||
| images (.gif, .jpg files) | ||
| audio (.wav files) | ||
| video (.mpg, .mov files) | ||
| *definition of �ordinary� in this context: | ||
| images display in a browser; audio/video files require a widely-available plug-in (e.g., MS Media Player) | ||
| Pages are ordinary, but ephemeral � a faster version of the �newspaper archive� problem | ||
| weather data | ||
| stock-market data | ||
| flight arrival/departure data | ||
| Pages are extraordinary though accessible | ||
| PDF (Portable Document Format) files � Adobe Acrobat Reader [has become �ordinary�] | ||
| Postscript files (the choice in computer science) | ||
| Flash, Shockwave, dynamic graphics | ||
| programs (executables, .exe) | ||
| compressed files (.zip, .tar) | ||
| Technically, these can be indexed; economically, they cannot. | ||
| Pages are extraordinary and not accessible� the Really Invisible Web� at least for now. | |||
| Pages that (may) require a sign-in, for example | |||
| The New York Times (required by site) | |||
| eBay, Amazon.com, Travelocity, TowerRecords (required by visitor) | |||
| Pages are extraordinary and not accessible� the Really Invisible Web� at least for now. | |||
| Pages that (may) require a sign-in | |||
| Data (really �databases�) that must be reached through forms (text boxes, radio buttons, etc.) in a Web page, for example | |||
| towerrecords.com | |||
| amazon.com� �The Infinite Regress� problem | |||
| Well, a few years ago, Google didn�t exist. | |
| AltaVista had no images in its index. | |
| Now both offer images as �ordinary.� | |
| Surely, PDF, Postscript, and the like are just around the corner, at least in Internet years. | |
| Can databases be far behind? |