The Enhanced E-R Model

Objectives

• Define terms
• Understand use of supertype/subtype relationships
• Understand use of specialization and generalization techniques
• Specify completeness and disjointness constraints
• Develop supertype/subtype hierarchies for realistic business situations
• Develop entity clusters
• Explain universal (packaged) data model
• Describe special features of data modeling project using packaged data model

 

 

 

Supertypes and Subtypes

• Enhanced ER model: extends original ER model with new modeling constructs
• Subtype: A subgrouping of the entities in an entity type that has attributes distinct from those in other subgroupings
• Supertype: A generic entity type that has a relationship with one or more subtypes
• Attribute Inheritance:
• Subtype entities inherit values of all attributes of the supertype
• An instance of a subtype is also an instance of the supertype

 

 

 

Relationships and Subtypes

• Relationships at the supertype level indicate that all subtypes will participate in the relationship
• The instances of a subtype may participate in a relationship unique to that subtype. In this situation, the relationship is shown at the subtype level

 

 

 

Generalization and Specialization

• Generalization: The process of defining a more general entity type from a set of more specialized entity types. BOTTOM-UP
• Specialization: The process of defining one or more subtypes of the supertype and forming supertype/subtype relationships. TOP-DOWN

 

 

 

Constraints in Supertype/ Completeness Constraint

• Completeness Constraints: Whether an instance of a supertype must also be a member of at least one subtype
• Total Specialization Rule: Yes (double line)
• Partial Specialization Rule: No (single line)

 

 

 

Constraints in Supertype/ Disjointness constraint

• Disjointness Constraints: Whether an instance of a supertype may simultaneously be a member of two (or more) subtypes
• Disjoint Rule: An instance of the supertype can be only ONE of the subtypes
• Overlap Rule: An instance of the supertype could be more than one of the subtypes

 

 

 

Constraints in Supertype/ Subtype Discriminators

• Subtype Discriminator: An attribute of the supertype whose values determine the target subtype(s)
• Disjoint – a simple attribute with alternative values to indicate the possible subtypes
• Overlapping – a composite attribute whose subparts pertain to different subtypes. Each subpart contains a Boolean value to indicate whether or not the instance belongs to the associated subtype

 

 

 

Entity Clusters

• EER diagrams are difficult to read when there are too many entities and relationships
• Solution: Group entities and relationships into entity clusters
• Entity cluster: Set of one or more entity types and associated relationships grouped into a single abstract entity type

 

 

 

Packaged Data Models

• Predefined data models
• Could be universal or industry-specific
• Universal data model = a generic or template data model that can be reused as a starting point for a data modeling project (also called a “pattern”)

 

 

 

Advantages of Packaged Data Models

• Use proven model components
• Save time and cost
• Less likelihood of data model errors
• Easier to evolve and modify over time
• Aid in requirements determination
• Easier to read
• Supertype/subtype hierarchies promote reuse
• Many-to-many relationships enhance model flexibility
• Vendor-supplied data model fosters integration with vendor’s applications
• Universal models support inter-organizational systems

 

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體能活動的健康益處

任何年齡的人士要促進健康，其中一種最好的方法就是多做運動。

兒童及青少年

科學證據的強度	健康益處
非常有力	改善心肺耐力及肌力 較理想的身體成分（脂肪百分比） 改善骨骼健康 改善心血管及新陳代謝健康的生物性指標
中等強度	減少焦慮及抑鬱徵狀

成年人及長者

科學證據的強度	健康益處
非常有力	降低早逝的風險 降低患上心臟病的風險 降低中風的風險 降低患上二型糖尿病的風險 降低患上高血壓的風險 降低出現不理想血脂譜的風險 降低患上代謝綜合症的風險 降低患上結腸癌的風險 降低患上乳癌的風險（女性） 預防體重上升或促進體重減輕（須配合適當的飲食） 改善心肺功能及肌力 預防跌倒 減低抑鬱情緒 較佳的認知能力（長者）
中等強度至非常有力	較佳的身體功能（長者） 減少中央肥胖
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batch file script - check folder / file size

@echo off

fc  c:\ABC\abc.txt c:\DEF\abc.txt > nul
if errorlevel 2 goto err2
if errorlevel 1 goto err1
if errorlevel 0 goto err0

goto exit

:err0
echo. is same
goto exit

:err1
echo. is different
goto exit

:err2
echo. file is lost
goto exit

:exit

-----------------

rem：//這段編碼是用來比較檔案或資料夾的大小是否相同。

@echo off 
rem：//關閉指令行自身的顯示

fc  c:\ABC\abc.txt c:\DEF\abc.txt > nul
rem：// fc.exe 是用來比較兩個檔案或兩組檔案並且顯示其中的不同之處。(一般在 c:\windows\system32\)
rem：// 如要比較兩個資料夾，可以變為：( fc  c:\ABC\*.* c:\DEF\*.* > nul  )
rem：// 如路徑有空格，應變為：( fc  "c:\AB C\*.*" "c:\DE F\*.*" > nul  )
rem：// 假若不加 >nul ，cpu會飆到100。>nul 用於屏蔽標準輸出在屏幕上的顯示。

if errorlevel 2 goto err2 
rem：//表示兩個檔案中，有一個以上是不存在 
if errorlevel 1 goto err1 
rem：//表示兩個檔案不同
if errorlevel 0 goto err0 
rem：//表示兩個檔案相同

goto exit 
rem：//以上皆不是時直接跳到「:exit」行

:err0 
rem：//兩個檔案相同時執行此行
  echo. They are same
goto exit 
rem：//直接跳到「:exit」行

:err1
echo. They are different
goto exit

:err2
echo. Some file(s) is lost
goto exit

:exit
rem：//完結

Security responsibilities and responses: A user's view

1. Which of the following actions would help users to keep information safe?

Choose more than one option.

Keep important information stored separately in hard copy form

Have a strong password

Be careful about leaving your computer unattended

Report anything suspicious

2. Which of the following should be part of the effort to reduce the level of threat to security posed by an organization's own employees?

Choose more than one option.

Keep employees motivated

Ensure that employees' skills are updated on an ongoing basis

Monitor employee activity

Install appropriate technical barriers

3. Which of the following are key considerations for an information security program?

Choose more than one option.

Confidentiality

Availability

Communication

Integrity

4. Which of the following are criteria for a good password?

Choose more than one option.

It is almost impossible for others to guess

It has personal significance

You don't have to write it down

It evokes a pleasant, thus memorable, image



Topic title: Security responsibilities and responses: A user's view


Which of the following are considered potential security threats?

Computer viruses

Internet privilege

Loss of data

Unauthorized access

Introduction to security policies

1. Security ___________ define which of a company's resources are to be protected, whereas security _________ define how to protect them.

To fill the first blank, select one of the options below. The other option will automatically appear in the second blank.

procedures
policies



Security policies define which of a company's resources are to be protected, whereas security procedures define how to protect them.




2. Which of the following should be the first step in developing a security policy?

Choose an option.

Assigning risk factors
Prioritizing resources

Classifying resources

Defining acceptable and unacceptable activities



3. Which of the following statements best describes a company's information protection policy?

Choose an option.

It defines methods of remotely connecting to the main network
It provides guidelines on how users should process, store, and transmit sensitive information
It provides guidelines for reporting and managing virus infections
It defines the appropriate use of computing resources

Identifying Internet security measures

1. Which of the following involves users submitting their usernames and passwords in encrypted form?

Choose an option.

Anonymous access
Basic authentication

Secure authentication

Digital certificates


2. You use your ________ to decrypt messages you receive.

You send your _________ to the people from whom you expect to receive an encrypted message.

To fill the first blank, select one of the options below. The other option will automatically appear in the second blank.

private key
public key


You use your private key to decrypt messages you receive.

You send your public key to the people from whom you expect to receive an encrypted message.


3. A digital certificate contains which of the following?

Choose more than one option.

A certificate serial number

A certificate expiration date

Your private key

The certificate authority's digital signature