Such services generally allow people to provide personal information, then search for other individuals using criteria such as age range, gender and location. Most sites allow members to upload photos of themselves and browse the photos of others. Sites may offer additional services, such as webcasts, information technology chat, and message boards. Sites sometimes allow people to register for free but may offer military service which hurting for a monthly fee.
Various theories of interpersonal compatibility classify interpersonal relationships by grades of comfortability and consider them as dependent of personal traits (durable http://www.datingblack.org psychological parameters) and/or psychological types (or temperaments). Such approach is much beloved in pop psychology (astrological compatibility etc.)