What does it mean to be related? How do you define a relation's properties?

Suppose you are going to design an instant messaging application called Telegraph. Telegraph is a modularized application composed of UI module, Chat module, and Contact module. The UI module uses the Chat module and the Contact module to render the user interface. The Chat module deals with sending and receiving messages. The Chat module uses the Network module for network communication. When users send/receive messages via the network, the Chat module uses the Crypto module to encrypt/decrypt the message. The Contact module manages the contact list. It also uses the Crypto module for encryption/decryption. The Crypto module uses the Math module for calculation. Now we propose a metric to measure the stability of modules. Formally, we define the "stability" of a module i as Si = a+dut where di" (i.e., incoming connection or dependency) is the number of modules that directly or indirectly USES module i and d?ut (i.e., outgoing connection or dependency) is the number of modules that…

What are three cases when a surrogate key might be used in place of a relation's main key?

What are three signals that a surrogate key should be generated for the primary key of a relation instead of using the main key?

Consider sending a large file of F bits from Host A to Host B. There are three links (and two switches) between A and B, and the links are uncongested (that is, no queuing delays). Host A segments the file into segments of S bits each and adds 80 bits of header to each segment, forming packets of L=80+ S bits. Each link has a transmission rate of R bps. Find the value of S that minimizes the delay of moving the file from Host A to Host B. Disregard propagation delay.

QUESTION 3 A functor is a function symbol that names the relationship, but the name can be anything as long as it's a valid identifier. True False

explanation of three circumstances where a substitute key for a relation's primary key should be created?