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Middleware a layer of software whose purpose is to mask heterogeneity and to PROVIDE a convenient programming model to application PROGRAMMERS. Middleware is represented by processes or objects in a SET of computers that interact with each other to IMPLEMENT communication and resource sharing support for distributed applications.

Middleware a layer of software whose purpose is to mask heterogeneity and to provide a convenient programming model to application programmers. Middleware is represented by processes or objects in a set of computers that interact with each other to implement communication and resource sharing support for distributed applications.

• ARCHITECTURE MODEL
• Fundamental model
• INTERACTION model 
• FAILURE model 
• Security model

Confidentiality:

 Protection against disclosure to unauthorized individual. 

E.g. ACLs (access control lists) to provide authorized access to INFORMATION. 

Integrity: 

 Protection against alternation or corruption. 

E.g. changing the account number or amount value in a money ORDER 

Availability: 

Protection against interference TARGETING access to the resources. 

E.g. denial of service (DoS, DDoS) ATTACKS 

Non-repudiation:

Proof of sending / receiving an information.

E.g. DIGITAL signature

Confidentiality:

 Protection against disclosure to unauthorized individual. 

E.g. ACLs (access control lists) to provide authorized access to information. 

Integrity: 

 Protection against alternation or corruption. 

E.g. changing the account number or amount value in a money order 

Availability: 

Protection against interference targeting access to the resources. 

E.g. denial of service (DoS, DDoS) attacks 

Non-repudiation:

Proof of sending / receiving an information.

E.g. digital signature

ENCRYPTION: 

 E.g. Blowfish, RSA 

Authentication:

E.g. password, PUBLIC key authentication 

Authorization:

E.g. access control LISTS

Encryption: 

 E.g. Blowfish, RSA 

Authentication:

E.g. password, public key authentication 

Authorization:

E.g. access control lists

The degree to which a computer SYSTEM can be extended and re-implemented. 

IEEE = Institute of Electrical and Electronic Engineers 

e.g., IEEE 802.11 WLAN, IEEE 802.3 ETHERNET 

W3C = World WIDE Web Consortium 

e.g., HTML Recommendations

The degree to which a computer system can be extended and re-implemented. 

IEEE = Institute of Electrical and Electronic Engineers 

e.g., IEEE 802.11 WLAN, IEEE 802.3 Ethernet 

W3C = World Wide Web Consortium 

e.g., HTML Recommendations

• Ubiquitous COMPUTING used in single environment such as home or HOSPITAL. 
• Mobile computing has advantage when USING different DEVICES such as laptops and printers.

• DIFFICULTIES of developing distributed SOFTWARE
• NETWORKING problems
• Security problems

• Performance
• Distribution
• RELIABILITY (fault TOLERANCE)
• INCREMENTAL GROWTH
• Sharing of data/resources
• Communication

1. Heterogeneity 
2. Openness 
3. SECURITY 
4. SCALABILITY 
5. Failure handling 
6. CONCURRENCY 
7. Transparency

MOBILE: COMPUTING devices are being CARRIED around.

UBIQUITOUS: Little computing devices are all over the place.

Mobile: Computing devices are being carried around.

Ubiquitous: Little computing devices are all over the place.

• The INTERNET
• INTRANETS
• MOBILE and UBIQUITOUS COMPUTING

• Programs are executed concurrently 
• There is no GLOBAL time 
• COMPONENTS can FAIL independently (ISOLATION, CRASH)

A distributed system is a collection of INDEPENDENT computers that APPEARS to its users as a single COHERENT system. A distributed system is ONE in which components located at networked communicate and coordinate their actions only by passing message.

A distributed system is a collection of independent computers that appears to its users as a single coherent system. A distributed system is one in which components located at networked communicate and coordinate their actions only by passing message.