| Characteristic |
Nature |
Implications
for Complex
Realtime Systems |
| The
Cell |
All biological systems are object
oriented in design. The most basic object is the Cell. The Cell contains
the DNA which is interpreted to perform various actions required by the
cell. |
State Machine is the most basic
building block of complex real-time systems. The code executed to run
through the state machine is equivalent of the DNA in a cell. |
| Cell
Aggregation |
Cells in the body join together to
form tissue. Tissues form different organs like stomach, lungs etc. Organs
form systems like Respiratory system, digestive system. |
Complex real-time systems would be
a sea of state machine objects interacting with each other. There will be
low level state machines which would work together to implement high level
state machine behavior. |
| Layered
Architecture |
The biological systems have a
layered architecture and interactions between objects at high level are
very well defined. For example the interactions between the stomach and
intestines are fairly well defined. However there are hardly any
interactions between a cell in the stomach and a cell in the intestine.
The interactions take place at clearly defined interface points. |
Complex systems should be designed
in a layered fashion. The system is divided into sub-systems with clearly
defined interfaces between sub-systems. Very few objects in a sub-system
should interact with objects in the other sub-system. For example, a
telephone switching system would consist of call processing, maintenance,
O&M sub-systems. Most objects in the call processing sub-system will
interact only with other objects in the same sub-system. |
| Cell
Inheritance |
Cells in the human body have the
same basic structure with a cell wall, cytoplasm, nucleus, DNA, RNA etc.
Individual cells have further refinements to the basic structure to
perform the specific function assigned to them. |
In complex real-time systems all
state machine objects in a sub-system share common characteristics. These
characteristics can be abstracted in a common base state machine class.
The individual state machines inherit from the base state machine class.
For more details, refer to the article on state
machine inheritance. |
| Organism
Inheritance |
Most of the animal and plant
kingdoms are organized as a deep hierarchy. Animals and plants are
organized as families. For example, the cat family contains the lion, cat,
tiger etc. |
Extremely complex systems will
probably never get developed from scratch. Such products would be
developed by refining and recombining existing, well tested products. All
products based on the same basic products would form a product
family. |
| Evolution
and Mutation |
All biological systems have
evolved over a millions of years, with each generation evolving to better
adjust to the changing environment. Most changes take place gradually but
sometimes there were quite sudden and major changes caused by mutations. |
The only way to develop complex
software systems is to follow an evolutionary software release development
schedule. The first release implements the basic cross-section of the
system. Subsequent releases refine the software in small steps. This
development lifecycle minimizes development risk by integrating the
product at every stage of development.
Sometimes sudden changes in business environment, technology or competitive
landscape require sudden changes, similar to mutations.
|
| Animal
and Plant Kingdoms |
Most complex living organisms on
Earth fall into animal and plant classifications. From organization point
of view, plants are completely distributed system with no centralized
control. Animals have centralized control in form of a central nervous
system and brain. |
Complex Realtime systems can
generally be designed with two techniques:
- Distributed processing with overall centralized control (Animal). In
such systems a central processor would keep track of overall operation
of the system.
- Distributed processing with little or no centralized control
(Plant).
|
| Asynchronous
Communication |
Most interactions in nature are
asynchronous, i.e. the initiator of the interaction is free to process
other interactions while waiting for a response. In many cases the send
message and the response are processed quite independently. |
Most interactions in Realtime
systems are already asynchronous in nature. i.e. sender of a message
doesn't block to receive the response. Other messages will be processed by
the sender. A response will be processed as and when it is received. This
contrasts with communication techniques like CORBA, RPC where the sender
blocks till a response is received. |
| Immune
System |
Most biological systems are able
to recover from a large number of fault conditions. These cases range from
re-growing organs, recovering from a cut in the skin to fighting with
invading virus and bacteria.
Due to these "fault handling" techniques the human body is
able to recover from most fault conditions. We need to see a doctor only
if the natural defenses fail.
|
As man made systems increase in
complexity, the systems will need to be capable of recovering from all
kinds of software and hardware failure conditions. This will become
essential as cost of maintaining complex systems would be prohibitive if
the operator is expected to fix every little problem in the system.
|
| Load
Sharing Redundancy |
Nature rarely uses one-for-one
redundancy. Most redundant systems are load sharing, e.g. lungs, liver
etc. |
We have seen an increasing trend
towards load sharing over one-for-one redundancy. In general load sharing
systems scale better with increasing load. Failure of a load sharing
system will never knock out the complete system. |
| Emotions
and Unpredictable Behaviour |
Complexity and random,
unpredictable behavior go hand in hand. Most higher order organisms
exhibit emotions and unpredictable behavior. |
As man made systems become more
and more complex, systems will sometimes behave in completely
unpredictable fashion. This would happen because it is impossible to test
a complex system completely. As complexity increases, so will the
number of untested scenarios.
So be prepared to baby sit the system during sleepless tension filled
nights!
|
