Database Reference
In-Depth Information
ratings, and comments. A title, a category, a set of keywords (tags), and a textual
description are also provided by the user who added the video. A list of related
videos is generated by YouTube, which consists of links to other videos that have a
similar title, description, or tags, and are thus supposedly similar in content. Uploa-
ders may also specify a set of related videos of their choice.
YouTube provides a dedicated feature to share videos on other online commu-
nities (e.g., Facebook [
6
], Twitter [
7
], MySpace [
8
]) and makes it easy to embed
them in an external Web page by automatically generating the required HTML code.
2.2.2 Flickr
Flickr
[
2
] is a popular photo-sharing Web site that allows users to store, search, and
share their photos with family, friends, and the online community. Flickr, hosted on
62 databases across 124 servers, manages about 800,000 user accounts per pair of
servers and contained more than 5 billion images as of August 2009.
Launched in February 2004 by a Vancouver-based company, Flickr was origi-
nally a multiuser chat room, called “FlickrLive”, with the capability of exchanging
photos in real time. In March 2005, Flickr was acquired by Yahoo! and became a
photo-sharing Web site allowing users to upload, share, and view photos freely. In
March 2009, the ability to upload and view HD videos was also added to Flickr's
features.
Users can join the Flickr network by means of two account types. Free accounts
allow users to upload 100 MB of images in a month and at most 2 videos. However,
free account users can manage at most 200 photos in their photostream. A photo can
be added to at most ten groups, and statistics about photos are not accessible. A free
account is automatically deleted when it has been inactive for 90 consecutive days.
“Pro accounts”, characterized by unlimited storage, allow users to upload any number
of images and videos every month and to access account statistics. Furthermore, each
image can be added to up to 60 groups. However, pro account users are charged a
yearly fee of about 25 dollars.
Flickr, as a photo-sharing Web site, provides both private and public image
storage. Private photos are visible by default only to the photo owner. By contrast,
public photos are viewable by all Flickr users. In addition, each user maintains a list
of “favorite photos” on the Flickr Web site, which is publicly visible to the user's
contacts when they log into Flickr. However, they can also be marked as viewable
by friends and/or family. Furthermore, for each uploaded image, belonging to either
the private or the public category, the user (photo owner) can define a “contact list”
to control image access for a specific set of users.
Flickr users, characterized by common interests, can gather to form self-organized
communities, referred to as groups. The main purpose of groups is to facilitate the
sharing of user photos in the group pool, i.e., a collection of photos shared by any
member with the group. There are three types of groups: (a) public, where anyone
can see the group photo pool, and anyone can join it, (b) public, where anyone can
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