prova

Question 1

• What are the 3 conceptual layers?

Answer 1

presentation layer, application layer, resource manager layer

Question 2

• Pros and cons TOP-down approach?

Answer 2

pro: focus on high level goals, addresses functional and non-functional requirements
con: can only be applied if the IS is developed from scratch

Question 3

• Explain bottom-up approach:

Answer 3

1 - define access channels and client platforms
2 - examine existing resources and their functionality (RM layer)
3 - wrap existing resources, integrate them into consistent interface (AL layer)
4) adapt output of AL for client (P layer)

Question 4

• why is bottom-up a good approach?

Answer 4

Design focuses on integration/reuse of existing (legacy) systems/applications. It is not an advantage to use it, but a necessity

Question 5

• Name the 4 distribution alternatives (understand them all):

Answer 5

transaction as unit of distribution, application as unit of distribution, db operation as unit of distribtuion, middleware controls distribution

Question 6

transaction as unit of distribution pros and cons:

Answer 6

pro: simple and easy solution. works in heterogeneous environments
cons: inflexible, limited scope, transaction restricted to single node

Question 7

application as unit of distribution. Pros and cons:

Answer 7

pros: locaIIty processing. Supports application reuse.
cons: inflexibility regarding data access operations. Complex program model. db access operations cannot reach across multiple nodes\

Question 8

db operation as unit of distribution. Pros and cons:

Answer 8

pro: high flexible for data access
con: increase communication onverhead, program model complexity

Question 9

middleware controls distribution:

Answer 9

pros: high flexible data access,simple and powerful programing model
cons: increased communication overhead, schema integration required

Question 10

• what are the five components of CORBA ?

Answer 10

transactional client, transactional server, recoverable server, object request broker, transactional service (OTS)

Question 11

• in the corba, which components receive prepare command?

Answer 11

transactional service (OTS) and recoverable server

Question 12

• what are the 3 approaches for coupling database and programming language?

Answer 12

static embedded sql, dynamic embedded sql, and call level interface CLI

Question 13

• why is SQLJ binary portable?

Answer 13

java is a platform independent language. The use of SQLJ-precompiler/translator avoids DBMS-SPECIFIC precompiler technology. Therefore, compiled SQLJ application is portable.

Question 14

• which coupling database approach jdbc uses?

Answer 14

CLI

Question 15

• Which approaches sqlj uses?

Answer 15

embedded sql with binary portability

Question 16

• which approach uses early query compilation and is vendor-specific?

Answer 16

static-embedded sql

Question 17

• explain how the components of db-gw support access to multiple database at the same time:

Answer 17

the Driver Manager manages interactions between Applications and Drivers and it is capable of realize n:m-relationship between application and drivers. It loads the drivers for the multiple databases and it maps the data sources to the drivers.

Question 18

• PROS call-level interface (cli) static, and dynamic sql

Answer 18

pros: avoids vendor-specific pre-compiler (binary portable program)

Question 19

• PROS AND CONS static embedded sql (early query compilation)

Answer 19

pro: performance
con: vendor specific pre-compiler. Code resulting from pre-compiler is not portable

Question 20

• CONS dynamic embedded sql (late query compilation)

Answer 20

con: vendor specific pre-compiler. Code resulting from pre-compiler is not portable

Question 21

• explain the difference between orthogonal persistence and independence persistence

Answer 21

in orthogonal persistence the persistence is independent of data type, class. Instances of the same class may be transient or persistent.
Independence persistence, also known as transparent persistence, the code operating on transient and persistent objects is basicaly the same. There is no impact on the client object when interacting with persistent objects. There is no special codign for implementing persistence.

Question 22

• what are the 2 peristent components for entity beans?

Answer 22

Bean Manager Persistence (BMP)

CMP

Question 23

• which mechanism requires developers to write the code for the database access call?

Answer 23

Bean manager persistence - BMP

Question 24

• WSDL - which sub-element contains the address of the service’s location?

Answer 24

endpoint

Question 25

* WSDL - which subelement refers to the protocol for message transport?

Answer 25

binding

Question 26

* WSDL - what XML standard is used to specify the type element?

Answer 26

XMLSchema

Question 27

- WSDL - what are the protocols that can be used with SOAP?

Answer 27

SOAP is transport independent. Any protocol: HTTP, HTTPS, SMTP…

Question 28

- what are the elements of a SOAP message?

Answer 28

root element:Envelop | sub elements: fault, header, and body elements

Question 29

- which element is mandatory to exist in a SOAP message

Answer 29

body element

Question 30

- WHAT are the 4 techniques to manage sessions?

Answer 30

HTTP authentication, cookies, hiding fields in forms, URL enconding

Question 31

- describe pros and cons from the 4 techniques to manage session:

Answer 31

hiding fields in form: pro: supported by every browser and browser configuration. con: increase complexity of the application and the response time suffers. http authentication: adv: automatically supported by browsers and web-servers. cons: user registration and authentication before every session cookies: adv.: automatically included in web server interaction by the browser. disadv: it can be disabled by the browser url encoding: adv: supported by all browsers and configurations. disadv: realization is complex. personalized url is not user friendly.

Question 32

- name advantages and disadvantages of asynchronous transaction processing compared to synchronous single transaction:

Answer 32

advantages of asynchronous: If the server is down or a connection error occurs, the client can keep processing and putting messages on the queue. it is easier to implement load balance. It’s possible to create a prioritization of the requests disadvantages: requests may not be directly authorized and executed. The server response can take more time to return to client.

Question 33

Question: Sometimes we lazy replication with a very long delay practiced (eg 8h). Describe a scenario where did makes sense .

Answer 33

?

Question 34

- name 3 approaches to realize change data capture:

Answer 34

snapshot, log based, trigger based, audit columns

Question 35

- CUPID schema-element named AvgRoomPricePerNight. Name and perform the 4 steps to normalize it:

Answer 35

tokenize: avg room price per night expand: average room price per night eliminate: average room price night tagging: average (static) room (hotel) price (money) night (time)

Question 36

- SCHEMA INTEGRATION: name the four properties that a integrated schema should have and describe how it can be violated

Answer 36

minimal, complete, correct, intelligible

Question 37

- why ACID is too strict for a complex workflow? what are the alternatives to support transactions in workflow?

Answer 37

only appropriate for individual activities or restricted subset of activities (atomic spheres)

Question 38

- describe the schema reference architecture for the federated DBMS:

Answer 38

external schema, federated schema, export schema, component schema, local schema

Question 39

Name the 6 types of heterogeneity and explain them:

Answer 39

Technological heterogeneity, data model heterogeneity, schematic heterogeneity, structural heterogeneity, syntatic heterogeneity, semantic heterogeneity

Question 40

Pick ONE appropriate distribution alternative (1..4) for each approach of unit of distribution: DataBase Gateway, Web-Service, Federated DBMS, RMI/RPC, TP Monitor

Answer 40

db gw: db operation federated dbms: middleware as unit of distribution TP Monitor: middleware controlling distribution RMI/RPC - application as unit of distribution Corba: application as unit of distribution web-service: application as unit of distribution

Question 41

Name 3 database gateways coupling approaches and say if each of them: code or binary compatible, early or late compiled

Answer 41

Static embedded sql (early compiled, source compatible) dynamic embedded sql (late compiled, source compatible) call level interface (CLI) (late compiled e binary compatible)

Question 42

Single-master lazy-replication scheme with 1 master and 2 slaves is used Name advantages and disadvantages

Answer 42

Adv: If a connection error occurs or if a slave is down, the master still works. As it uses a master with 2 slaves, it avoids conflicts. disadvantages: data in replicas may be not updated. Therefore, if updated data is required, you cannot use the slaves as a source to read data.

Question 43

Name 3 advantages and disadvantages of CLI

Answer 43

Adv: Portability, uniform data access, flexibility disadv: performance and increases application complexity.

Question 44

in which states of the Entity_beans life cycle is persistent state managed by entity manager?

Answer 44

Managed and removed

Question 45

pessimistic locking

Answer 45

requires long read locks to avoid lost updates

Question 46

optimistic locking

Answer 46

Does do not guarantee consistent reads, inconsistencies may arises if entities are not protected by a version attribute.

Question 47

Application Server | Name 2 approaches to achieve scalability in terms of processes

Answer 47

* scaling up a server system (caching and resource pooling) * scaling out by adding more machines

Question 48

application server: Give two examples of pooling

Answer 48

stateless bean pooling, DB connection pooling

Question 49

Name and explain an approach that helps scaling stateful session beans

Answer 49

Passivation, the bean state is saved on disk so the bean in the memory can be reused by another client

Question 50

Web Service Coordination: What component services are offered by a coordination service?

Answer 50

activation service, registration service, and coordination protocols.