计算机代写|ST207 Database

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这是伦敦政经学校数据库课程的代写成功案例。

ST207课程简介

This course is compulsory on the BSc in Data Science. This course is available on the BSc in Actuarial Science, BSc in Mathematics, Statistics and Business and BSc in Politics and Data Science. This course is available with permission as an outside option to students on other programmes where regulations permit and to General Course students.

This course has a limited number of places (it is capped). Students who have this course as a compulsory course are guaranteed a place. Places for all other students are allocated on a first come first served basis.

Prerequisites 

The goal of this course is to cover basic concepts of database management systems, including relational and other types of database management systems.

The topics covered will include basic concepts of the relational model, creating and modifying relations using Structured Query Language (SQL), basic SQL queries using SELECT operator, nested queries, aggregate operators such as GROUP BY, integrity constraints and relations, views, application development using JDBC, Internet protocols such as HTTP and XML, storage and indexing, tree-structured indexing using B+ trees, hash-based indexing, query evaluation and algorithms for relational operations, external sorting, transaction management and concurrency, database schema and normal forms, and overview of NoSQL databases such as key-value stores, document, and graph databases.

ST207 Database HELP（EXAM HELP， ONLINE TUTOR）

A chalkboard provides:
Create-Use chalk to write on the board.
Read-Look at the board.

Update-Simply erase old data and write new data.
Delete-Just erase the old data.
A chalkboard has the following advantages over a book:
CRUD-It’s easier to create, read, update, and delete data.

Retrieval-Although a chalkboard doesn’t provide an index, it usually contains much less data than a book so it’s easier to find what you need.
Consistency-Keeping the data consistent isn’t trivial but again, because there’s less data than in a book, you can find and correct any occurrences of a problem more easily.

Easy Error Correction-Correcting one error is trivial; just erase it and write in the new data. Correcting systematic errors is harder, but a chalkboard contains a lot less data than a book, so fixing all of the mistakes is easier.

Backups-You can easily back up a chalkboard by taking a picture of it with your cell phone. (This is actually more important than you might think in a research environment where chalkboard discussions can contain crucial data.)

Ease of Use-A chalkboard is even easier to use than a book. Toddlers who can’t read can still scribble on a chalkboard.
Security-It’s relatively hard to steal a chalkboard nailed to a wall, although a ne’er-do-well could take a cell-phone picture of the board and steal the data. (In some businesses and schools, cleaning staff are forbidden to erase chalkboards without approval to prevent accidental data loss.)

Sharing-Usually everyone in the room can see what’s on a chalkboard at the same time. This is one of the main purposes of chalkboards.
A book has the following advantages over a chalkboard:
Persistence-A chalkboard is less persistent. For example, someone brushing against the chalkboard may erase data. (I once had a professor who did that regularly and always ended the lecture with a stomach covered in chalk.)
Low Cost and Extensibility-Typically, books are cheaper than chalkboards, at least large chalkboards.

Portability-Books typically aren’t nailed to a wall (although the books in the Hogwarts library’s restricted section are chained to the shelves).
The following database properties are roughly equivalent for books and chalkboards:

Validity-Neither provides features for validating new or modified data against other data in the database.

Speed-Both are limited by your reading (and writing) speed.

Atomic Transactions-Neither provides transactions.

ACID-Neither provides transactions, so neither provides ACID.

Ability to Perform Complex Calculations-Neither can do this (unless you have some sort of fancy interactive computerized book or chalkboard).
In the final analysis, books contain a lot of information and are intended for use by one person at a time, whereas chalkboards hold less information and are tools for group interaction. Which you should use depends on which of these features you need.

A recipe card file has the following advantages over a book:
CRUD-It’s easier to create, read, update, and delete data in a recipe file. Updating and deleting data is also more aesthetically pleasing. In a book, these changes require you to cross out old data and optionally write in new data in a place where it probably won’t fit too well. In a recipe file, you can replace the card containing the old data with a completely new card.
Consistency-Recipes tend to be self-contained, so this usually isn’t an issue.
Easy Error Correction-Correcting one error in the recipe file is trivial; just replace the card that holds the error with one that’s correct. Correcting systematic errors is harder but less likely to be a problem. (What are the odds that you’ll mistakenly confuse metric and English units and mix up liters and tablespoons? But you can go to https://gizmodo.com/ five-massive-screw-ups-that-wouldn’t-have-happened-if-we-1828746184 to read about five disasters that were caused by that kind of mix-up.)

Backups-You could back up a recipe file fairly easily. In particular, it would be easy to make copies of any new or modified cards. I don’t know if anyone (except perhaps Gordon Ramsay or Martha Stewart) does this.

Low Cost and Extensibility-It’s extremely cheap and easy to add a new card to a recipe file.
Security-You could lose a recipe file, but it will probably stay in your kitchen most of the time, so losing it is unlikely. Someone could break into your house and steal your recipes, but you’d probably give copies to anyone who asked (except for your top-secret death-bychocolate brownie recipe).
A book has the following advantages over a recipe file:
Retrieval-A recipe file’s cards are sorted, essentially giving it an index, but a book also provides a table of contents. With this kind of recipe file, it would be hard to simultaneously sort cards alphabetically and group them by type such as entrée, dessert, aperitif, or midnight snack.

Persistence-The structure of a recipe file is slightly less persistent than that of a book. If you drop your card file down the stairs, the cards will be all mixed up (although that may be a useful way to pick a random recipe if you can’t decide what to have for dinner).
The following database properties are roughly equivalent for books and recipe files:
Validity-Neither provides features for validating new or modified data against other data in the database.
Speed-Both are limited by your reading and writing speeds.
Atomic Transactions-Neither provides transactions.
ACID-Neither provides transactions, so neither provides ACID.
Ease of Use-Many people are less experienced with using a recipe file than a book, but both are fairly simple. (Following the recipes will probably be harder than using the file, at least if you cook anything interesting.)

Portability-Both books and recipe files are portable, although you may never need your recipes to leave the kitchen.
$>$ Sharing-Neither is easy to share.

Ability to Perform Complex Calculations-Neither can do this. (Some computerized recipe books can adjust measurements for a different number of servings, but index cards cannot.) Instructional books usually contain tutorial information, and you are expected to read them in big chunks. A recipe file is intended for quick reference and you generally use specific recipes rather than reading many in one sitting. The recipe card file is more like a dictionary and has many of the same features.

ACID stands for Atomicity, Consistency, Isolation, and Durability.
Atomicity means transactions are atomic. The operations in a transaction either all happen or none of them happen.
Consistency means the transaction ensures that the database is in a consistent state before and after the transaction.

Isolation means the transaction isolates the details of the transaction from everyone except the person making the transaction.
Durability means that once a transaction is committed, it will not disappear later.

BASE stands for the distributed database features of Basically Available, Soft state, and Eventually consistent.
Basically Available means that the data is available. These databases guarantee that any query will return some sort of result, even if it’s a failure.
Soft state means that the state of the data may change over time, so the database does not guarantee immediate consistency.

Eventually consistent means these databases do eventually become consistent, just not necessarily before the next time that you read the data.

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