Collected Concepts Flashcards
(39 cards)
1
Q
Types of Maintenance
A
- Corrective change
- Adaptive change
- Perfective change
- Preventive change
2
Q
Corrective Change
A
- Deals with the repair of faults or defects found in day-today system functions
3
Q
Adaptive Change
A
- Implementing changes in a part of the system, which has been affected by a change that occurred in some other part of the system.
- Business or Environment causes
4
Q
Perfective Change
A
- implementing new or changed user requirements
- involves making functional enhancements to the system
- Increase the system’s performance
5
Q
Preventive Change
A
- Involves performing activities to prevent the occurrence of errors
- Tends to reduce the software complexity
- Improves program understandability
- Increases software maintainability
6
Q
Top-Down Code Reading
A
- Use context and prior assumptions to gain overall understanding from selected details
- Examining high-level structuring of system
- Create hypotheses from these
- Go progressively deeper into the code, looking for evidence for or against
7
Q
Top-Down Strategy Aim
A
- Squeeze maximum useful information out of each examination of the system
- At each examination of the system, just look for the smallest useful unit of information
8
Q
Top-Down Exploit Beacons
A
- Cues that suggest instant hypotheses
- Should stand out (be visible at a glance)
9
Q
Top-Down Exploit System Diagrams
A
- Give an overview of the program
- Hide unimportant and distracting details
- Only useful for code reading if can be automatically generated (or if very small)
10
Q
Top-Down Strategy Key Features
A
- Importance of context and prior understanding
- Confirms domain assumptions through verification reading
- Don’t need to understand every word to understand overall meaning
- Meaning is brought to print, not extracted from print
11
Q
Bottom-Up Code Reading
A
- Start with individual statements and build up picture incrementally
- Applies when class/method/etc to be examined already identified
- Skim over code, looking for recognisable idioms
- Form abstract view of the task of the idiom
- Combine recognised units to make conjectures about ever larger sections of code
12
Q
Bottom-Up Code Reading Cons/Pros
A
- Pros
- Gives detailed understanding of fragments of code
- Cons
- Can be difficult to understand full meaning of fragments without knowing their context
- Difficult to know where to start, if program is big or unfamiliar
13
Q
Opportunistic/Hybrid Code Reading
A
- A hybrid of top-down and bottom-up
- Begin with top-down, to gain the overview
- Then selectively apply bottom-up, when nearing ‘code-level’
- Presence of beacons can indicate opportunity for change in strategy
14
Q
Program Slicing
A
- Understand how particular variable got its value, at particular point in the program
- Remove all program statements that don’t affect the value at this point
15
Q
Data Dependency Graphs
A
- Create graph from code
- 1 node for each program statement
- Directed edges between nodes indicate patterns of variable usable and dependency
16
Q
Control Flow Graphs
A
- Create graph from code,
- 1 node for each program statement and directed edges between nodes
- Indicate patterns of control flow between consecutive statements
17
Q
Code idiom
A
- Language-independent way of expressing a construct that is frequently used.
- Idioms are helpful in bottom-up code reading
- Recognisable
- Can be used as a starting point for knowledge about program behaviour, which can be built up.
18
Q
Coding Conventions
A
- Language-specific best-practice guidelines
- Code that conforms to conventions is easier to comprehend
19
Q
Swap idiom
A
- Two variables need to swap values
- Will most likely look something like this: t = a; a = m;
20
Q
Process Every Item in Collection Idiom
A
- Language-independent statement of idiom:
- curr := first item in collection
- while not at end of collection do
- process curr
- curr := next item after curr end while
- end while
21
Q
Search Collection Idiom
A
- Search a collection for the first item that has satisfies the given property:
- curr := first item in collection
- found := false
- while not at end of collection and not found do
- if curr has required property
- found := true
- item := curr
- curr := next item after curr
- if curr has required property
- end while
22
Q
Control Dependency Graphs
A
- 1 node for each program statement
- Directed edges between nodes indicate dominant control relationships between statements (not only consecutive statements as in CFG)
23
Q
Evolutional Design
A
- Comes from agile but has wider applicability
- At the local code level, evolutionary design involves refactoring
- At the system code level, test-driven design can be used, following a red-green-refactor process.
- These sorts of evolutionary design techniques help us address the failings of BUFD, as they correspond to a just-enough, just-in-time approach.
- I.e. they don’t assume that we will get everything right the first time
24
Q
Code Smell
A
- A code smell is evidence present in a piece of code that suggests it could be improved.
- With regards to evolutionary design, in which we continually aim to move towards a better design, code smells can be used to identify places where refactoring should be done.
25
Open Source Dangers
* Open source code can disappear or have breaking changes made without warning.
* There is likely to be no official company behind it who can send a representative to either implement the part of the system where the open source code is needed, or teach your employees how to use it.
* Do not have 24/7 technical support if something goes wrong, no one is responsible for it, other than yourself.
26
Forward migration
* Initial migration of the entire database, followed by installation of a forward gateway
* Migrates unchanged legacy apps forward onto a modern DBMS and then migrates the legacy apps to new target apps.
* One initial Cold Turkey step
* Involves forward DB gateway
27
Reverse Migration
* Database migration is done at the end of the process. Target apps are created and installed on a reverse gateway that permits access to the legacy DB
* Target app calls must be migrated in reverse direction, back onto the legacy database, until the legacy database is subsequently migrated
* Permits more time to prepare database migration compared to forward
* Determine minimal amount of legacy data to migrate
* Gateway capabilities may be added "just in time"
28
General Migration
* Combination of forward and reverse migrations.
* Gateway is more complex, contains functions of forward, reverse, mappable table and coordinator.
* Permits DB migration step to be incremental and parallel with the other steps
29
Legacy Information System (IS)
Any information system that significantly resists modification and evolution to meet new and constantly changing business requirements
30
Cold Turkey Migration Strategy
Rewriting legacy IS from scratch to produce target IS, using modern techniques and hardware
* Problems:
* A better system must be promised
* Business conditions never stand still
* Specifications rarely exist
* Undocumented dependencies frequently exist
* Legacy ISs can be too big to cut over data
* Management of large projects is hard
* Lateness is seldom tolerated
* Large project tend to bloat
* Homeostasis is prevalent
* Analysis paralysis sets in.
31
Chicken Little Migration Strategy
Migration Legacy IS by small incremental steps until the desired long-term objective is reached
* Each step requires small resource allocation.
* Produces small result toward the desired goal - an increment
* Incremental migration methodology
* Pros
* Less Risky
* If something fails, its only one step at a time
* Outlook is optimistic, not unpredictable until deadline like in Cold Turke)
32
Decomposable Architecture
Interfaces, applications and database services can be considered distinct components with well-defined interfaces.
* Applications modules must be independent of each other (have not hierarchal structure, and interact only with the DB)
* Gateways can be placed between application modules and legacy database service.
* Called database gatewat
33
Semidecomposable Architecture
* Only user and system interfaces are separate modules
* Applications and DB are not separate from each other
* Analysis and migration are more complex and error-prone
* Gateway placed between interfaces and the rest of the legacy IS
* Called Application Gateway
34
Nondecomposable Architecture
* No functional components are separateble
* Worst architecture for migration
* End users and ISs interact directly with one, unstructured, component or module
* Gateway encapsulates the entire legacy IS.
* Called IS gateway.
* Most complex.
* Primary means for dealing with the user interface.
35
Hybrid architecture
* During software evolution, Legacy IS might had parts that fell into different architecture categories
36
Gateways
Software module between operational software components to mediate between them.
* Insulate certain components from changes being made to other components
* Translate requests and data between the mediated components
* Coordinate between mediated components for update consistency.
37
Forward Gateway
* Enables legacy applications to access DB environment on the target side of the migration process
* Translate legacy calls forward to target calls.
38
Reverse Gateway
* Enables target applications to access legacy data management environment.
* Translate target calls in the reverse direction back into legacy calls.
39
