System Definiton
one or more components of differing nature
The individual components interact with one another via internal interfaces
fulfils a defined purpose by providing or executing functions
A system progresses through a life-cycle, from the development to the realisation, commissioning, operation until its disposal
In order to define a system, it must be delineated
system boundary separates the system and its components from the system environment
components interact via external interfaces with the system environment
The system environment is not part of the system
The components of a system can be systems themselves
They are then referred to as subsystems
The complete system is then also termed a System-of-Systems (SoS)
The separation can occur on the same level and/or in a hierarchical fashion
System Grenzen
System Structures
Complexity of Systems
no objective definition for complexity
some properties correlate with higher complexity
comparison of transistor count and size of instruction sets of various processors
Combinatorial explosion of the state space of comparatively small state machines executed in parallel
Failure
Any deviation of a function’s behaviour from its (intended) specification is a failure of the function or service
Failures are caused by errors in the components of a system
Error
An error is an internal system state that deviates from the expected state necessary to perform a function/service and always occurs at run time of the system
The occurrence of an error can lead to a propagation of further errors inside the system
When a propagating error reaches the system boundary it causes a failure
The reason for the occurrence of an error is a fault
Fault
An active fault is a fault that causes an error during run time of the system
Otherwise the fault is still present in the system but is in a non-activated or dormant state (so-called dormant fault)
An external fault acts on components of a system from outside the system boundary
The external fault either by itself or by activating an existing internal fault, causes an error in the system
The internal fault is also termed a vulnerability in this context
Fault Classes
Development faults
Physical faults
Interaction faults
natural faults
malicious faults
operational faults
occur during the development of a system
only affect physical components
include all external faults
Natural faults
arising from natural phenomena
Malicious faults
intentionally brought into a system
affect a system from outside in order to inhibit its operation
make it possible to gain control over it
Operational faults
faulty interactions of a user with the system
during run time
Failure Modes
type of deviation from a specified service when a failure occurs
content failure
timing failure
silent failure
(in)consitsnt failures
magnitude of failure
Deviation of the content of information
Deviation of the timing
complete absence of delivered information due to termination of the service
(in)consistent failure
Whether the failure is experienced by all users of the service in the same way (consistent failure) or in differing ways (inconsistent failures)
Propagation of Failure
system consisting of more than one component
When a component experiences a failure due to a fault, this can cause further failures in the dependant components
worst case, a chain reaction occurs that propagates to the system boundary, causing a system failure
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