PolyU ENG2003 知识点整理

IoT: networks of physical devices embedded with sensors, software, and connectivity that enable data collection and exchange.

Sensing: comprises objects that generate data, which are then reported to servers via wired or wireless communication links.

Networking and Data Communications: an efficient and reliable network to deliver data and commands among connected objects and servers.

Applications: data processing that normally takes place on computer clusters or the cloud.

Cyber-Physical System (CPS): Advanced IT Integration

Data consists of the raw facts and figures that can be processed into information.

Information is data that has been summarized or otherwise manipulated for use in decision making.

Nyquist Sampling Theorem: To ensure the sampled signals are still distinguishable from one another, The sampling frequency f_s should be at least twice the highest frequency contained in the signal.

Quantization is the process that confines the amplitude of a signal into a finite number of values.

Aspect Ratio = W / H

Assembly Language Programming

Advantage: less complicated than machine language. Usually generate more efficient code than high level languages.
Disadvantage: need the understanding of CPU structure. Still difficult to program.
Application: sometimes use in the programming of embedded systems (e.g., Micro controller (MCU) in printer, washing machines, etc.).

High-level Language Programming

Advantage: need the least amount of effort to write a program.
Disadvantage: the program written may not be optimal (depends on the compiler) .
Application: for large scale programs.

Primary Storage (Volatile)

Registers: A small amount of very fast memory blocks located inside the CPU chip.
Cache Memory: A special group of fast memory circuitry located on or close to the CPU. Its function is to speed up processing by temporarily storing data and instructions that may soon be needed by the CPU at a “handy” location, such that the CPU access to them quickly.
Random Access Memory (RAM):
- provides temporary storage commands
- data from input devices
- information ready to be sent to output
- currently running programs/their data
- intermediate data generated by the currently running programs

Driver and Drive

Driver: a program that tells an operating system how to communicate with a hardware component.
Drive: a term used to describe a storage device.

OSI Model

Physical Layer – Physical connection to medium
Data Link Layer – Hop-by-hop physical transmission
Network Layer – End-to-end data delivery
Transport Layer – Process-to-process data delivery
Session Layer – Logging users on and off; Dialogue control
Presentation Layer – Data formatting, encryption, and compression
Application Layer – Logical connection to host

Four Phases of DHCP Operations

Server discovery
IP lease offer
IP lease request
IP lease acknowledgement

Three levels to understand database:

The place where data is stored: Hardware.
Database Management System: MS Access, SQLite, MySQL, etc.
Database application: ERP, banking systems, etc.

Transaction: a collection of operations that form a single, indivisible, logical unit of work.

ACID properties:

Atomicity: a transaction is either fully done or fully rolled back.
Consistency: integrity constraints, both explicit and implicit, should be always met before and after the execution of a transaction.
Isolation: a transaction should be executed independently of one another, and cannot see the uncommitted changes of another running transaction.
Durability: once a transaction has been completed, the updates to the database must persist even if there are software or hardware failure afterwards.

RDBMS: relational database management system, including MySQL, PostgreSQL, Oracle, or Microsoft SQL Server.

Data modelling: the process of creating a specific data model for a determined problem domain.

Data model: a relatively simple representation of more complex real-world data structures.

Entity: a person, place, thing, or event about which data will be collected and stored.

Strong Entity: an entity is said to be existence-independent if it can exist apart from all of its related entities.
Weak Entity: its primary key is partially or totally derived from the parent entity.
Associative Entity: an entity used to bridge two entities for their M: N relationship.

Attribute: a characteristic of an entity.

Relationship: describes an association among entities.

Weak Relationship: primary key of the child entity does not contain a primary key component of the parent entity.
Strong Relationship: primary key of the child entity contains a primary key component of the parent entity.

Participation:

Optional Participation: one entity occurrence does not necessarily require corresponding entity occurrence.
Mandatory Participation: one entity occurrence requires corresponding entity occurrence.

Constraint: a restriction placed on data, e.g., a student’s GPA must be between 0.00 and 4.30.

Row: 行，represents a single entity occurrence, or an instance of the entity.

Column: 列，represents one attribute of the entity, required to have a name and a data type.

INT: for storing integers without any decimal component.
NUMERIC (p, d): for storing decimal values.
- p: the maximum number of digits.
- d: the maximum number of digits to the right of the decimal point.
CHAR (n): fixed-length character data where n specifies the target length.
VARCHAR (n): variable-length character data where n specifies the maximum length.
DATE: for storing the date information containing a four-digit year, month, and day of the month.
TIME: for storing the time of a day (hour, minute, second).
TIMESTAMP: for storing the combination of date and time.

Key: one or more attributes

Primary Key: a candidate key selected to uniquely identify all other attribute values in any given row.
Superkey: an attribute or combination of attributes that uniquely identifies each row in a table.
Candidate Key: a minimal (irreducible) superkey.
Foreign Key: the primary key of one table that has been placed into another table to create a common attribute and link the two tables.

Firewall Types:

Packet Filtering Firewall: if a packet matches the packet filter’s set of rules, the packet filter will drop or accept it.
Stateful Inspection Firewall: monitors the state of the network connections.
Firewall Gateway: works like a proxy and can understand certain applications and protocols.

Integrity Rules of Keys:

Entity Integrity:
Requirement: the primary key is unique and not null.
Purpose: each row has a unique identity, and foreign key values in a table can properly reference primary key values in another table.
Example: no invoice can have a duplicate number, nor can it be null.
Referential Integrity:
Requirement: a foreign key may have either a null entry, or a valid entry matching a primary key value of the related table, i.e., every non-null foreign key value must reference an existing primary key value.
Purpose: make it possible to delete a row in one table whose primary key has mandatory matching foreign key values in another table.

SQL: Structured Query Language, a standard programming language used to manage and manipulate relational databases.

SQL Statement: instruction used to perform various operations on databases.

CREATE

CREATE TABLE table_name 
( 
    column_name1 data_type , 
    column_name2 data_type, 
    column_name3 data_type, 
    .... 
);

Setting constraints:

CREATE TABLE Orders ( 
    OrderID int NOT NULL, 
    OrderNumber int NOT NULL, 
    PersonID int, 
    PRIMARY KEY (OrderID), 
    FOREIGN KEY (PersonID) REFERENCES Persons(PersonID) 
);

SELECT

SELECT O.OrderID, C.CustomerName, O.OrderDate 
FROM Orders AS O 
INNER JOIN Customers AS C 
ON O.CustomerID=C.CustomerID 
ORDER BY O.OrderDate;

GROUP BY Day
BETWEEN 50 AND 60
WHERE City IN (‘Paris’, ’London’)
Aggregation Functions: COUNT, AVG, SUM, MIN, MAX