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ISD Exam 1 Review
Terms in this set (46)
Rounded box, data is transformed/manipulated
Point-to-point communications to packet switching
Point-to-point: join machines with wire and agree how to exchange info by using voltage/current, but needs a lot of wires and involves changing wires
Packet switching: several machines share a single communication channel (wire) and packets are made up of the info
Divided interconnected tech and challenges (different types of computers for example) and layer them, each layer depends on layers below it. There are 7 layers
Number of bits transmitted per second
Delay between sending a request and receiving a response
When was the first message sent on the internet?
First packet switching network
Networks that transmit packets of information.
Do messages in a packet-switched network between the same two computers always follow the same routes?
No, the routes constantly change depending on instantaneous traffic estimates.
What makes the information exchange between computers using packets so robust?
Each Gateway is connected with several other nodes, providing for multiple paths to a destination.
Benefits of packet switching
-Pack switching allows several machines to share a single communication channel.
-In packet switching the wiring doesn't need to be changed whenever a different pair of computers want to exchange information.
-Packet switching optimizes the use of the expensive communication channels required to send them.
How to tell modem acting as router
Mentions LAN connection
Which of the following is a reason for latency in a connection?
The website server requires many relays to send messages back and forth.
The server of the website is experiencing a heavy amount of requests resulting in bottlenecks.
Data Flow Diagrams (DFDs)
Show analyst where info comes from and where it is stored, eliminates redundancies, illustrates where data is exchanged, Gane-Sarson approach used (entity, process, data store, data flow)
Entity (external agent)
Box, supplies or consumes data, ex: customer, supplier
Rounded box, data is transformed or manipulated, ex: fix errors, submit work
Arrow, info moving between two objects, be specific and concise, ex: complaint, rules
Three-sided box, data kept for a period of time
Rules for DFDs
1. Always start/end with an entity or data store, not a process
2. Have at least 1 inflow
3. Cannot connect an entity and data store without a process in between
4. Processes must have inflow and outflows
5. Never repeat processes
6. Data flows are named as descriptive nouns, NO VERBS
7. Cannot connect two entities or two data stores
Entity Relationship Diagrams (ERDs)
Graphical technique used to organize/analyze info, represents relational databases, illustrates to businesses how entities relate
DFDs vs. ERDs
DFD: show how data is exchanged/flows
ERD: show how data is stored
Series of tables related through primary and foreign keys. Data storage technique that's a table with each column a element and the row ONE specific entry of that element
A unique identifier, each table must have one
Crows feet = many
0 = none
| = one
|| = one and only one
|o = 0 or 1
Read by saying the cardinality then the name of the ERD object closest
Not allowed, when crows feet on both sides
Normalizing the ERD
1. No attributes are a list (one only)
2. Non-primary keys must be dependent on a primary key
3. Non-primary keys are not dependent on any other non-primary keys
Need a permanent IP address and new domain name, http is insufficient since it's subject to man-in-the-middle attack where they take your info (The attacker poses as a router or switch, but reads the traffic as it passes by), https is secure (3rd party)
Code developed and debugged by others, evaluate carefully before using
Keep files short, well-labeled, separate PHP and HTML, try to only have 6-12 files in a directory
Leveling a DFD
Make it more detailed
When one entity refers to an instance of another entity, such as an order referring to the originating customer, the entity stores the other entity's unique identifier as an attribute
What do you need in order to run a public web server from an Iowa City appartment?
A reasonable computer, free software and a web connection with a permanent IP address
Source control software
Manages different versions of the software created by different members of the software team to help members share changes as they are made
Involves writing functions to check each function or unit of code automatically
Open-source relational database , creates databases, responds to queries, builds tables, allocates user permissions. Most users work with the data manipulation language rather than the data definition language.
SQL (Structured Query Language)
Involves data definition and data manipulation
Create, alter, drop, show
Defines database structure and what info is stored
Select, delete, update, insert
Defines info added, retrieved, updated, or deleted
INSERT INTO () VALUES ()
MySQL words vs number formatting
quote words, don't quote numbers
Used for ROWS IN TABLES
Finds alphabetical matches
Matches T or S
Group By operator
Columns selected for output
Sort in ascending/descending order
Not Null vs Null
Not Null: won't allow empty cells
Null: allows column cell to be empty, default
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