is there someone who knows what the acronym "M3DA" (the M2M-protocol defined by the Mihihni developers) stands for? I'm just not able to find anything on that, maybe I'm blind - or is there just no fixed meaning behind it?
Thanks in advance!
M3DA: A protocol optimized for the transport of binary M2M data, which is made available in the Mihini project.
M2M + Mihini = 3M
&
DA=data
That's all.
Related
Has anyone tried implementing a new transport for Rebus? How much work is involved? E.g. number of interfaces that needs to be implemented? Assuming a sensible transport mechanism is used such as Greg Youngs event store..
Thank you.
As the aptly named #user1121956 says, it's a matter of implementing IDuplexTransport, which is just bringing ISendMessages and IReceiveMessages together.
As you can see, the two interfaces boil down to two methods, so when I say that it's a lot of work to implement a new transport, it's because it's not trivial to implement those methods.
It doesn't mean that it's not possible, it's just that it's a place where you would need to be very careful to get things right - otherwise, messages might be dropped or other bad things might happen, and that would not be cool :)
With that said - if you feel like you're up to it ;) - I suggest you check out the Rebus source code and look into the contract tests for the transports - this is where a bunch of common scenarios get run against all the officially supported transports. A good starting point would be to extend the tests with a GregsEventStoreTransportFactory.
I will be happy to help you out with guidance along the way if you run into trouble!
I've been programming in Delphi with Midas/DataSnap for quite long time and quite happy with it. Moving to .NET I'm more than happy with the ADO.NET DataSet. For CRUD application, I'm highly uncomfortable with any kind of ORM. Generic data-structure with automatic diff/delta handling get my job done better for me, an average database application developer.
Tried to study Java years ago, and could not find similar idea implemented. The closest I could find is SDO (Service Data Object). I thought it should be widely adopted when I saw it, but I'm wrong. Even the spec is rather old now, I still hardly find many people discuss on it or use it extensively. Assuming from information I can find on the internet, SDO usage is highly passive.
Wondering if it's dying ? Any experience in SDO you want to share ? Manual DTO coding is always better ?
Ok. I see. The answer is "no"
;)
Same for me when trying SDO first time. Old specs, passive feedback... Definitely NO.
I wouldn't recommend using SDO unless it's imposed on you by some other part of the project.
WebSphere process server uses SDO. It's not really a bad API once you learn it. But the spec and the documentation are vague. It doesn't spell out what happens if you ask for a field that doesn't exist, or whether it does type conversions while getting or setting fields, to name two gripes.
I don't think the API defines how to define new types, so that part will be implementation-specific. Type definitions are based on XSD, so you'll be working with those and all of the associated standards.
As others have implied, the API isn't widely used. This means it'll be hard to find people experienced with it, or help using it.
Imagine you have a channel of communication that is inherently lossy and one-way. That is, there is some inherent noise that is impossible to remove that causes, say, random bits to be toggled. Also imagine that it is one way - you cannot request retransmission.
But you need to send data over it regardless. What techniques can you use to send numbers and text over that channel?
Is it possible to encode numbers so that even with random bit twiddling they can still be interpreted as values close to the original (lossy transmittion)?
Is there a way to send a string of characters (ASCII, say) in a lossless fashion?
This is just for fun. I know you can use morse code or any very low frequency binary communication. I know about parity bits and checksums to detect errors and retrying. I know that you might as well use an analog signal. I'm just curious if there are any interesting computer-sciency techniques to send this stuff over a lossy channel.
Depending on some details that you don't supply about your lossy channel, I would recommend, first using a Gray code to ensure that single-bit errors result in small differences (to cover your desire for loss mitigation in lossy transmission), and then possibly also encoding the resulting stream with some "lossless" (==tries to be loss-less;-) encoding.
Reed-Solomon and variants thereof are particularly good if your noise episodes are prone to occur in small bursts (several bit mistakes within, say, a single byte), which should interoperate well with Gray coding (since multi-bit mistakes are the killers for the "loss mitigation" aspect of Gray, designed to degrade gracefully for single-bit errors on the wire). That's because R-S is intrinsically a block scheme, and multiple errors within one block are basically the same as a single error in it, from R-S's point of view;-).
R-S is particularly awesome if many of the errors are erasures -- to put it simply, an erasure is a symbol that has most probably been mangled in transmission, BUT for which you DO know the crucial fact that it HAS been mangled. The physical layer, depending on how it's designed, can often have hints about that fact, and if there's a way for it to inform the higher layers, that can be of crucial help. Let me explain erasures a bit...:
Say for a simplified example that a 0 is sent as a level of -1 volt and a 1 is send as a level of +1 volt (wrt some reference wave), but there's noise (physical noise can often be well-modeled, ask any competent communication engineer;-); depending on the noise model the decoding might be that anything -0.7 V and down is considered a 0 bit, anything +0.7 V and up is considered a 1 bit, anything in-between is considered an erasure, i.e., the higher layer is told that the bit in question was probably mangled in transmission and should therefore be disregarded. (I sometimes give this as one example of my thesis that sometimes abstractions SHOULD "leak" -- in a controlled and architected way: the Martelli corollary to Spolsky's Law of Leaky Abstractions!-).
A R-S code with any given redundancy ratio can be about twice as effective at correcting erasures (errors the decoder is told about) as it can be at correcting otherwise-unknown errors -- it's also possible to mix both aspects, correcting both some erasures AND some otherwise-unknown errors.
As the cherry on top, custom R-S codes can be (reasonably easily) designed and tailored to reduce the probability of uncorrected errors to below any required threshold θ given a precise model of the physical channel's characteristics in terms of both erasures and undetected errors (including both probability and burstiness).
I wouldn't call this whole area a "computer-sciency" one, actually: back when I graduated (MSEE, 30 years ago), I was mostly trying to avoid "CS" stuff in favor of chip design, system design, advanced radio systems, &c -- yet I was taught this stuff (well, the subset that was already within the realm of practical engineering use;-) pretty well.
And, just to confirm that things haven't changed all that much in one generation: my daughter just got her MS in telecom engineering (strictly focusing on advanced radio systems) -- she can't design just about any serious program, algorithm, or data structure (though she did just fine in the mandatory courses on C and Java, there was absolutely no CS depth in those courses, nor elsewhere in her curriculum -- her daily working language is matlab...!-) -- yet she knows more about information and coding theory than I ever learned, and that's before any PhD level study (she's staying for her PhD, but that hasn't yet begun).
So, I claim these fields are more EE-y than CS-y (though of course the boundaries are ever fuzzy -- witness the fact that after a few years designing chips I ended up as a SW guy more or less by accident, and so did a lot of my contemporaries;-).
This question is the subject of coding theory.
Probably one of the better-known methods is to use Hamming code. It might not be the best way of correcting errors on large scales, but it's incredibly simple to understand.
There is the redundant encoding used in optical media that can recover bit-loss.
ECC is also used in hard-disks and RAM
The TCP protocol can handle quite a lot of data loss with retransmissions.
Either Turbo Codes or Low-density parity-checking codes for general data, because these come closest to approaching the Shannon limit - see wikipedia.
You can use Reed-Solomon codes.
See also the Sliding Window Protocol (which is used by TCP).
Although this includes dealing with packets being re-ordered or lost altogether, which was not part of your problem definition.
As Alex Martelli says, there's lots of coding theory in the world, but Reed-Solomon codes are definitely a sweet spot. If you actually want to build something, Jim Plank has written a nice tutorial on Reed-Solomon coding. Plank has a professional interest in coding with a lot of practical expertise to back it up.
I would go for some of these suggestions, followed by multiple sendings of the same data. So that way you can hope for different errors to be introduced at different points in the stream, and you may be able to infer the desired number a lot easier.
I've been looking for open source examples of SOA applications, but most of the times I find simple tutorial hello world style examples that introduce the tricks of the respective middleware.
Do you have any suggestion about any middle to big size example with multiple layers and/or governance ? Isn't it some kind of common example (a la Lena in image processing) for SOA ?
Any suggestions ?
Thanks
What you may want to do is look at OpenESB:
http://wiki.open-esb.java.net/Wiki.jsp?page=OpenESBIntroductionTutorial
Once you have a working example then you can look at extending it yourself, as you will have the tools to do that, and see how you can get applications to work together.
Are you trying to learn how to use SOA or do you want to look at an architectural diagram where it has been used in a complex system?
The introduction above is for learning to use it, via OpenESB, I don't know where you may find a diagram of a large example of SOA.
It may help if you could narrow your question down to what precisely are you looking for.
I do not know of a detailed example you seek. If you are taking an approach of learning how to use SOA by checking examples, it may be a bad approach. You need to first know what and how you are going to do your SOA and then see what features are are enough for your needs.
I want the equivalent online resource to DNS in Twenty-One Days. I need one evening's reading that will explain what the different record types do, how do propagation and caching work, what is an SoA, etc.
I don't want anything that begins by explaining what DNS is.
Can anybody please point me in the right direction to find some online 'DNS for Geniuses' guide, please?
Check out DNS for Rocket Scientists
It does start with a very brief "What DNS is" but you can easily skip that.
You can also check out Records 101 which gives a good overview of the different record types - the examples are specific to DNSMadeEasy though.
I keep DNS and BIND on my bedside table. It was good to get me going (I used the TOC and skipped the "What is DNS" bits), and it keeps on giving me confidence and a helping hand.
I don't normally buy soot-on-dead-trees books, but this one is a rare exception that has repaid me many times over.
The definitive source, and quite readable (IMO):
http://www.ietf.org/rfc/rfc1035.txt
When I set up DNS for the first time I read DNS HOWTO. It worked pretty well for me.