MY-ASSIGNMENTEXPERT™可以为您提供units ST207 Database数据库课程的代写代考和辅导服务！
这是维多利亚大学 数据库课程的代写成功案例。
NIT1201课程简介
This unit introduces fundamental concepts and principles of database and explains its role and purpose in information system design and analysis. Students gain mastery of standard techniques to identify system requirements and design a simple database system. Content includes: systems concepts; role of the analyst; Systems Development Life Cycle (SDLC), process modelling, Entity-Relationship (ER) modelling; relational database design using ER and Extended ER modelling, SQL (Structured Query Language), normalisation; and database management systems (DBMS).
Prerequisites
On successful completion of this unit, students will be able to:
- Describe the benefits and functions of databases and their applications;
- Design a database using key relational database model concepts;
- Develop and apply entity relationships (ER) and extended entity relationships (EER) diagrams;
- Implement a relational database with multiple tables using a relational DBMS;
- Apply query languages and manage a database using SQL; and
- Normalise relations in a relational database system.
NIT1201 Database HELP（EXAM HELP， ONLINE TUTOR）
What does the CAP theorem say? Under what conditions is this not a “pick two of three” situation?
The CAP theorem says that a distributed database can guarantee only two out of three of the following properties:
Consistency-Every read receives the most recently written data (or an error).
Availability-Every read receives a non-error response, if you don’t guarantee that it receives the most recently written data.
Partition tolerance-The data store continues to work even if messages are dropped or delayed by the network between the store’s partitions.
This need not be a “pick two of three” situation if the database is not partitioned. In that case, you can have both consistency and availability, and partition tolerance is not an issue because there is only one partition.
Suppose Alice, Bob, and Cindy all have account balances of $\$ 100$ and the database does not allow an account’s balance to ever drop below $\$ 0$. Now consider three transactions: (1) Alice transfers $\$ 125$ to Bob, (2) Bob transfers $\$ 150$ to Cindy, and (3) Cindy transfers $\$ 25$ to Alice and $\$ 50$ to Bob. In what order(s) can those transactions be executed successfully?
If transaction 1 occurs first, then Alice tries to transfer $\$ 150$ to Bob and her balance drops below $\$ 0$, which is prohibited.
If transaction 2 occurs first, then Bob tries to transfer $\$ 150$ to Cindy and his balance drops below $\$ 0$, which is prohibited.
So, transaction 3 must happen first: Cindy transfers $\$ 25$ to Alice and $\$ 50$ to Bob. Afterward Alice has $\$ 125$, Bob has $\$ 150$, and Cindy has $\$ 25$.
At this point, Alice and Bob have enough money to perform either transaction 1 or transaction 2.
If transaction 1 comes second, then Alice, Bob, and Cindy have $\$ 0, \$ 275$, and $\$ 25$, respectively. (If he can, Bob should walk away at this point and quit while he’s ahead.) Transaction 2 follows and the three end up with $\$ 0, \$ 125$, and $\$ 175$, respectively.
If transaction 2 comes second, then Alice, Bob, and Cindy have $\$ 125$, $\$ 0$, and $\$ 175$, respectively. Transaction 1 follows and the three end up with $\$ 0, \$ 125$, and $\$ 175$, respectively.
Therefore, the allowed transaction orders are 3-1-2 and 3-2-1. Note that the final balances are the same in either case.
Explain how a central database can protect your confidential data.
If the data is centralized, then it does not remain on your local computer. In particular, if your laptop is lost or stolen, you don’t need to worry about your customers’ credit card information because it is not on your laptop.
Be sure to use good security on the database so cyber-criminals can’t break into it remotely. Also don’t use the application on an unsecured network (such as in a coffee shop or shopping mall) where someone can electronically eavesdrop on you.
What does the following check constraint on the SalesPeople table mean?
$(($ Salary $>0)$ AND (Commission $=0))$ OR $(($ Salary $=0)$ AND (Commission $>0))$
This constraint means that all salespeople must have a salary or work on commission but they cannot have both a salary and receive commissions.
MY-ASSIGNMENTEXPERT™可以为您提供units ST207 Database数据库课程的代写代考和辅导服务！
