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System design 2 (Data Controls (Security and Audit (Logical Security…
System design 2
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Data Design
The objective of data design is to define a set of flexible data structures that will enable the realization of the functional requirements agreed during requirements engineering, by supporting the input, output and process designs.
Normalisation
this is a technique that designers use to derive flexible, robust and redundancy free data structures
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accurately reflect values as per the original source from which the data was derived or that are consistent with any changes made in the system
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Code Design
Uniqueness - the designer must ensure that there could never be two identical values of the code relating to different data records
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Expand ability - A coding system should always allow for future growth in terms of the number of unique codes that can be generated
Length - This is an extension of the other considerations. if a code is not long enough - then it may not provide enough unique values to allow for future growth, and hence, the format of future codes may need to change to allow for more unique values
Faceted codes
A faceted code is one that is made up of a number of parts, or facets, such as vehicle registration identification numbers
Self-checking codes
This is the most common validation check performed on codes is to look up the code in some reference data table or file to determine whether it exists or not.
Network Database
is a more flexible derivation of a hierarchical database. Instead of each data node being linked to just one parent node, it is possible to link a node to multiple parents, thus forming a network-like structure
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Probably the best known examples of a network DBMS are IDMS (Integrated Data Management System) and IDS (Integrated Data Store)
Relational Databases
The basic structure of the relational model is where information about a particular entity is represented in rows and columns, thus the relation in relational database refers to the various tables in the database (TUPLES)
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Physical files
When designing data file structures, two fundamental factors must be consdiered
- How to physically organise the data on a disk
- how to access / retrieve the stored data
File Organisations
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Binary Chop
This is whereby the program continually narrows down scope of records to check on the negative side, adding new records to a sequential file necessitates a complete re-organisation of the file each time, which can be extremely time-consuming
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Data Controls
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Security and Audit
In terms of security the options available to the designer can be broadly categorized as physical or logical security. However there is a further aspect to security design that is not about the prevention of access or loss of system artifacts, but concerns the tractability of user activity, systems audit
Physical Security
Locks, barriers. safes.security personnel, backup and recovery
Logical Security
measures involve aspects of the software that make up the system in order to protect the system and its data from unauthorized access, destruction or corruption.
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Process Controls - many systems enforce some form of process workflow, which can be explicitly captured in some form of state model, such as a UML state machine diagram or a state transition diagram
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Common Design patterns
Abstract Factory - Builder- Factory method - Virtual Proxy-Lazy initialisation - Prototype - Singleton - Structural Adapter Wrapper or Translator - Bridge -Composite - Decorator -Facade - Flyweight - Proxy - Behavioural Chain of responsibility - Command - Interpreter - Iterator - Mediator - memento - Observer publish/subscribe - State - strategy - Template method - Visitor