{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

geog475.3.23 - Weak entity sets sometimes a key or an...

Info icon This preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
e designates a weak entity set; the key come partially from this relationship (shown with a double diamond) Name Host name @ login primary domain Name Name In2 In1 Name Secondary domain hosts K2 K1 K2 K1 K3 colors Has favorites fans beers addr name name breweries Manf. by beers Manf addr manf name Weak entity sets – sometimes a key or an entity set comes not completely from its own attributes, but from the keys of one or more entity sets to which it is linked by a {many to one, one to one} relationship This is called a weak entity set . Login name = user name + host name (+ ip add of the host) [email protected] - The password table records the username, not the host (allows someone to login from more than one machine) Consider an IP add consisting of a primary domain, sub-domain and host
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
- Key for primary domain is its name - Key for secondary domain is its name + primary domain name - Key for host = host name + secondary domain name + primary domain name (this info is necessary to uniquely identify a host) - A key
Image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern