Best design pattern for a large number of options?

Hi,
I'm faced with the following straightforward problem, but I'm having trouble coming up with a design solution. Any suggestions?
Two items in the database can be related in three possible ways (temp replacement, permanent replacement, substitute). Each item has three possible stock levels. The user can select one of two items.
This comes out to 54 different prompts that need to be provided to the user (example: "The entered item has a preferrable temp replacement available that is in stock, sell instead of the entered item?", "The entered item is out of stock, but has a substitute item available, use instead?", etc. etc.)
Does anybody have a suggestion of a good design pattern to use? In the legacy system it was implemented with a simple case statement, but I'd like to use something more maintainable.
If anybody has any suggestions, I'd appreciate it.
thanks,

In the legacy system it was
implemented with a simple case statement, but I'd like
to use something more maintainable.Is it ever likely to change? If no, then a case statement is pretty maintainable.
How is the data retrieved? I'm guessing it's a decision tree: if the desired object is in stock, return it, otherwise look for a permanent substitute, &c. In this case, perhaps you have a retrieval object that implements a state machine internally: each call to the retrieval operation causes a transition to the next-best state if unable to fulfill the request.
If you do retrieve all possible data in a single query (and I hope not, as that would almost certainly be very inefficient), then think of some sort of "preference function" that could be used to order the results, and store them in a TreeMap or TreeSet ordered by that function.

Similar Messages

What is the best design pattern for this problem?

No code to go with the question. I am trying to settle on the best design pattern for the problem before I code. I want to use an Object Oriented approach.
I have included a basic UML diagram of what I was thinking so far.
Stated simply, I have three devices; Module, Wired Modem, and Wireless Modem.
In the Device Under Test parent class, I have put the attributes that are variable from device to device, but common to all of them.
In the child classes, I have put the attributes that are not variable to each copy of that device. The attributes are common across device types. I was planning to use controls in the class definition that have the data set to a default value, since it doesn't change for each serial number of that device. For example, a Module will always have a Device Type ID of 1. These values are used to query the database.
An example query would be [DHR].[GetDeviceActiveVersions] '39288', 1, '4/26/2012 12:18:52 PM'
The '1' is the device type ID, the 39288 is the serial number, and the return would be "A000" or "S002", for example.
So, I would be pulling the Serial Number and Device Type ID from the Device Under Test parent and child, and passing them to the Database using a SQL string stored in the control of the Active Versions child class of Database.
The overall idea is that the same data is used to send multiple queries to the database and receiving back various data that I then evaluate for pass of fail, and for date order.
What I can't settle on is the approach. Should it be a Strategy pattern, A Chain of Command pattern, a Decorator pattern or something else.
Ideas?

elrathia wrote:
Hi Ben,
I haven't much idea of how override works and when you would use it and why. I'm the newest of the new here.
Good. At least you will not be smaking with a OPPer dOOPer hammer if I make some gramatical mistake.
You may want to look at this thread in the BreakPoint where i trie to help Cory get a handle on Dynamic Dispatching with an example of two classes that inherit from a common parent and invoke Over-ride VIs to do the same thing but with wildly varying results.
The example uses a Class of "Numeric" and a sibling class "Text" and the both implement an Add method.
It is dirt simple and Cory did a decent job of explaining it.
It just be the motivation you are looking for.
have fun!
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

What is the best design pattern for top-down ws development..?

Hi,
What is the best design pattern for top-down development+ wsdl2service....?

elrathia wrote:
Hi Ben,
I haven't much idea of how override works and when you would use it and why. I'm the newest of the new here.
Good. At least you will not be smaking with a OPPer dOOPer hammer if I make some gramatical mistake.
You may want to look at this thread in the BreakPoint where i trie to help Cory get a handle on Dynamic Dispatching with an example of two classes that inherit from a common parent and invoke Over-ride VIs to do the same thing but with wildly varying results.
The example uses a Class of "Numeric" and a sibling class "Text" and the both implement an Add method.
It is dirt simple and Cory did a decent job of explaining it.
It just be the motivation you are looking for.
have fun!
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

What is the best design pattern for multiple instruments?

I have several PXI cards (DMM, O-scope, etc) that I want to create a master panel that can control all of the instruments individually, though not necessarily all at the same time (turn "instruments" on and off at will while the master vi continues to run). Is there one design pattern (master/slave, producer/consumer, etc.) that works better than another for this type of master panel? Are there other alternatives for this type of problem (VI Server, etc)?
I was hoping that I could save a bunch of time if I could start on the right path right off the bat!
Thanks,
-Warren

elrathia wrote:
Hi Ben,
I haven't much idea of how override works and when you would use it and why. I'm the newest of the new here.
Good. At least you will not be smaking with a OPPer dOOPer hammer if I make some gramatical mistake.
You may want to look at this thread in the BreakPoint where i trie to help Cory get a handle on Dynamic Dispatching with an example of two classes that inherit from a common parent and invoke Over-ride VIs to do the same thing but with wildly varying results.
The example uses a Class of "Numeric" and a sibling class "Text" and the both implement an Add method.
It is dirt simple and Cory did a decent job of explaining it.
It just be the motivation you are looking for.
have fun!
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

Best design idea for parallel DAQ (via GPIB), PID control and watchdog system

Hello!
I am a starter programmer in LabView, I already understand the basic ideas, and design patterns, like producer/consumer, events state machine, functional global variables, and so on, so the basics...
I started a project a few weeks ago, and first I wrote and tested all of the necessary subvi-s for my project, like the ones initializing my GPIB devices (a Keithley mux and a dvm), controlling/reading out the measured voltage/resistancy values from them, subvi for my Static Analog Output card (I have to drive 7 analog output channels, 4 has to be PID controlled regarding to some of the measured values from the GPIB devices), and another subvi for the analogue card, sending TTL watchdog signals out to my experiment in every 2 seconds.
Any idea is welcomed about suggesting the best design pattern for my project.
The main features of my program would be:
After starting the user interface the program starts with a start-up state, initializes the DAQmx channels and the GPIB devices. The program starts to read out different values from the GPIB devices, including 4 temperature values in every 3 seconds.
In the same loop (?), using PID control, the program sets the DC voltage values of 4 channels (3 to heating wires, 1 to a Peltier-heat pump) on the Static Waveform Analogue output card, the remaining 3 values are constants.
I have to send digital TTL watchdog signal to some relays from the same output card, changing its state in every 2 seconds (not the same rate as the GPIB values are read out).
When the 4 temperatures and the power values regarding to the heating wires are equilibrated after a few hours, the program goes into another state, and signals to the user, that the measurement can be started. During a measurement, I write out all of the measured values to a TDMS file, and there is also some basic calculations "on the fly", like a moving average.
After the measurement done, the user can swap samples, and the program goes into the above state, waiting for equilibration . and so on...
Do you think I should use a Producer/Consumer pattern with events? Or someone would recommend me a better design idea?
Thanks very much!
ps.: I read out lots of values from the Keithleys, so I put them in a cluster. I made a small test vi (attached without the GPIB comm subvi-s), just to test the GPIB comm. So this is the recent state of my project. (all other subvi-s tested and ready to use as I wrote above, like the DAQmx output part)
Attachments:
GUI_Calorimeter_control_image_v2.vi ‏284 KB

Okey
I think it is a better approach if I work first, and after I ask
I go with small steps. For first, now I just want to make a DAQ analog output loop, and parallel a watchdog loop sending out TTL in every 2 seconds.
The main loop in my project will iterate with approx. 10-15 seconds.
I want to check in my watchdog loop, if my main loop hangs up (in that case the PID control stops, but the danger is if the output voltages stay on).
After some readings, I have decided to use a functional global variable.
I have attached the vi, can someone give me advice, what would be the good solution for this purpose?
(I know it is a bit silly what I messed up with the shift registers in the bottom loop, it was some experimenting).
Thanks in advance!
Attachments:
watchdog_funcglobvariable.vi ‏12 KB
Global 1_stop.vi ‏4 KB
analog_output+Watchdog.vi ‏57 KB

Design Pattern for execution queue

Anyone know of any good design patterns for using a JMS Queue and MDB's
          as async
          execution queue which maintains execution order by some key


Enforced ordering on redelivery will be supported in the
          next release, but only if the application clamps the pipe-line
          size down to its minimum and the MDB pool size down to one.
          I don't think enforced ordering is supported in the current release.
          We are looking at least partially addressing the general design
          pattern below in the release after next. I don't think I can
          get away with being more specific. (Sorry.) Currently, I
          think something along the line of Larry's solution is the only way to
          accomplish it. Interestingly, the recent thread started
          by "[email protected]" on correlating requests and responses
          seems to be somewhat related.
          Tom, BEA
          Larry Presswood wrote:
          > Well you are both correct however we have something which works
          > however it does involve some threading primitives which generally is not
          > a good idea
          > inside wlas but seems to work.
          >
          >
          > Generally have a singleton on the server which has slots for each key
          > with message
          > numbering for each message and force a wait if message for key is out of
          > order
          > during fifo processing rules. IE do what things you can do in parallel
          > but gate for
          > the last step.
          >
          > I think there is a general remote execution pattern out there.
          >
          > The general problem to solve is this:
          >
          > In a messaging system you want to process messages for each key/session
          > in order however
          > with a large number of sessions its possible to parallel messages for
          > different sessions
          >
          > Otherewise you can either create custom queues or a topic with a
          > selector and then
          > create custom consumers which does not behave as well from a resource
          > perspective
          > as MDB's do.
          >
          >
          >
          >
          >
          >
          >
          > Nick Minutello wrote:
          >
          >>I may be completely wrong - but I think that Larry is referring to the inherant
          >>out-of-order message consumption that you get when using MDB pools to consume
          >>from a Queue.
          >>
          >>In short, the only design pattern here is to deploy the MDB to only one machine
          >>in the cluster - and set the pool size to 1.
          >>
          >>In-order execution is incompatible with the parallel execution that MDB's give
          >>you.
          >>
          >>-Nick
          >>
          >>
          >>
          >>Tom Barnes <[email protected]> wrote:
          >>
          >>
          >>>Hi Larry,
          >>>
          >>>Generally, I think it is best to have a seperate queue per key if the
          >>>
          >>>number of keys is small. This prevents starvation of a particular
          >>>message. For example when handling message-priority, low priority gets
          >>>
          >>>an MDB pool of size 1, high priority gets and MDB pool of size 10.
          >>>
          >>>Note that WebLogic JMS allows a queue to specify a sort-order keys based
          >>>on arbitrary message fields. Note that the in-flight message pipe-line
          >>>
          >>>between server and asynchronous clients is unsorted.
          >>>
          >>>Tom, BEA
          >>>
          >>>Larry Presswood wrote:
          >>>
          >>>
          >>>>Anyone know of any good design patterns for using a JMS Queue and MDB's
          >>>>
          >>>>
          >>>>as async
          >>>>execution queue which maintains execution order by some key
          >>>>
          >>>>
          >>>>
          >>
          >>
          >>
          >

Is there a design pattern for this?

I'm looking for a solution to a design problem I have.
For a restaurant booking system I need a number of different opening times describing when you can and cannot book. These opening times are essentially Jodatime Period objects. There's a set of opening times spanning a week and these are repeated for every week (a default set of opening times) however it's possible to override these opening times say for a specific day.
The domain model would be something like a Restaurant class holding 2 Lists of OpeningTime objects one for defaultOpeningTimes and the other for overiddenOpeningTimes the overidden ones get used if they exist for the requested time period. However the database model would be a bit messy as I'd have 2 lists mapping to the same table (OpeningTime). Is that a good idea? Perhaps there's a design pattern for this, if someone could point me in the right direction I'd be very grateful, or perhaps this is the best solution? Thanks!

jduprez wrote:
But why do you put the logic in the database too (I'm no DB expert and I didn't know these concepts until I read your post, but that's what a dynamic view based on derived values looks like to me): performance (1 round-trip instead of two)?Hi jduprez. Long time no speakee.
I guess part of it is that I spent many years as a DBA and modeller, and really appreciate what it's taught me about design. Also, databases are (or should be) designed from the ground up to provide data-directed requests optimally, and include all sorts of nice stuff like transaction handling that aid consistency, as well as speed.
That said: I HATE SQL. Think Coliseum, with that emblazoned in 60-foot high letters around its walls, and it might come close to just how much I hate that so-called "language". I hate its form; I hate it's inconsistencies; I hate the fact that something like what OP is trying to do is NOT an easy task (and might involve the creation of a table that simply contains Dates, just in order to satisfy Boolean logic).
However, once you work it out, a database view (at least from the database's standpoint; JDBC I'm not so sure about) is just like any other Table - and that I DO like.
Programs are good at processing parameterized (ugh) temporal information; databases are good at persistence and high volume. Those two may meet at some point, but I reckon it's going to take another Codd (or Joda) before it does.
- that's clearer to 90% of the dev team (my biased numbers, based on 50% of Java developers having decent knowledge of SQL and much less than that having the advanced SQL knowledge which I rank your suggestion at)Sounds to me like you'll get the solution that matches the skills you have then. Is that what you really want, if a better one is available?
- that doesn't require investigating the if of your suggestion (JDBC support)Agreed, but only because my JDBC knowledge isn't what it could be. I'd also be surprised if it doesn't support access to a named view, since they were designed to be equivalent to Tables.
- the Op is using DAOs, so it's possible, if profiling does show this is hampering performances, to change that with no impact on the client code that calls the DAO.There's no doubt that a database solution is much higher level than a programming one; but, as I said, it's what they were designed to do. And tinkering around with program optimization has the feel of a "hacker's solution" to me. Not that there's any particular problem with that - I do it quite often when I have no control over my source - but I also try to keep in mind what the "actual" problem is.
Winston

Choice of design pattern for data acquisition system

Hello all
I have a trouble about selecting the suitable design pattern / architecture for a data acquisition system.
Here is the details of the desired system:
There is data acquisition hardware and I need to use it by observing parameters on User interface.
the data acquisiton period, channel list to scan should be chosen on User interface. Besides, there are many user interface interactions. e.g. if user selects a channel to add scanlist, then I need to enable and make visible some other parts on user interface.
When user completes the channel selection, then he will press the button to start data acquisition. Then I also need to show the scanned values on a graph in real time and log them in txt file.
I know that I cannot use producer consumer pattern here. because the data acquisition loop should wait for parameters to scan channels. and it works in a given period by user. so the user interface loop performs higher rate then consumer loop (data acquisition loop). it means queue will be bigger bigger. if I use notifier it will loss some data come from user interface.
is there any idea about that ? is there any suitable design pattern for this case ?
Thanks in advance
best regards
Veli BAYAR
Embedded Systems Software and Hardware Engineer
"You live in a graphical world. Why not program in one?"
Solved!
Go to Solution.

johnsold wrote:
Veli,
I recommend the Producer/Consumer model with some modifications.
You might need three loops. I cannot tell for sure from your brief description.
The User Interface loop responds to the user inputs for configuration and start/stop of acquisition. The parameters and commands are passed to the Data Acquisition loop via a queue. In this loop is a state machine which has Idle, Configuration, Acquisition, and Shutdown states (and perhaps others). The data is sent to the Processing loop via a different queue. The Processing loop performs any data processing, displays the data to the user, and saves it to file. A notifier can be used to send the Stop or shutdown command from the User Interface loop to the other loops. If the amount of processing is minimal and the file write times are not too long, the Processing loop functions might be able to occur in the Timeout case of the UI loop Event structure. This simplifies things somewhat but is not as flexible when changes need to be made.
I am not sure that a Design Pattern for this exact setup exists but it is basically a combination of the Producer/Consumer (Events) and Producer/Consumer (Data) Design Patterns.
Lynn
Check out this thread: http://forums.ni.com/t5/LabVIEW/Multiple-poll-case-structures-to-event-help/td-p/2551309
There are discussions there about a 3-loop architecture that may help you.
Jeff
Jeffrey Zola

Design Pattern for multithreaded client server program

I asked this question in another post, but with other stuff, so I'll distill this one.
I am creating a multi-threaded client server program (just for learning - a chat program at this point). I built the server and client in swing, and I'm wondering what the best design pattern is for this setup. Right now all the swing stuff is in the MyServer class. In that class I have a loop accepting client connections to the serverSocket and creating a new MyServerThread (threaded client connection).
The problem is that all the work of creating input streams, interacting with the server, all that stuff is done in the MyServerThread class, but I want that text to be written up to the Swing objects - which is in the MyServer class. So right now in the MyServerThread class I pass the MyServer object into it, but I'm not sure if that is really the most robust thing to do. Does anybody have any suggestions as to how this should be done. If somebody has an article they'd like to point to I'll check it out too. But if it's just the run-of-the-mill multithreaded client-server article, I've read alot and most don't specifically address my question.

Thanks for the reply Kaj, and I think I'll keep my design for now, since it's just quick and dirty. I've read the MVC concept a while ago and I'll revisit it again when I get more serious. But I have a question, why should I be using a callback interface, why an interface at all? And then make MyServer implement that interface...why not just pass MyServer to the thread object? Or is there something down the line that I did not forsee?

Design Pattern for ATE

Looking for suggestions on the best design pattern (using OOP) for an automated test environment application. The current code (LabVIEW only, no Test Stand) has it's own UI and support VIs for selecting the test environment, sequence of tests to run, running a sequence, evaluating test results and outputting pass/fail reports (HTML) and test measurement result files (TDM). The intent was to give the developer a framework where he/she can concentrate on writing the actual tests. Unfortunately, in the environments where it is used, developers always find the framework lacking for their needs and so tend to have their own version by the time they are done. This thing does not scale well nor is it very flexible.
This framework was originally written with LV 6.1. I put it in a LV2011 Project, but it won't build due to its sheer bulk so it's being run strictly under the development environment (which I hate doing). The whole framework needs a face lift.
Any suggestions? I've looked at the AF but it seems "over-qualified" for this, plus I don't have a bunch of parallel processes in this case. Things run pretty much sequentially from the get go just by the nature of the testing.
“A child of five could understand this. Send someone to fetch a child of five.”
― Groucho Marx

You could create pure virtual class that defines your test step API. Methods for the class would consist of things like setup, teardown, execute to name a few. Your developers could use this base class as the template and API for their tests. The methods regulate the format of the data exchange between your engine and their test. I would also recommend that you use packed libraries so that your test steps are basically plugins. Your test sequence would need to contain the name of the appropriate plugin to use in order to invoke the correct test step. This model is flexible and easy to extend.
We are actually investigating using this same approach for our test system. Our current system uses TestStand and we are going to investigate TestStand 2012 ability to use dynamic dispatch to invoke our test steps. It should be interesting. We use other features of TestStand so it would be nice if we can make this work. In your case a LabVIEW only implementation should be fairly straightforward.
Mark Yedinak
"Does anyone know where the love of God goes when the waves turn the minutes to hours?"
Wreck of the Edmund Fitzgerald - Gordon Lightfoot

Design Pattern for Controlling Uniqueness

Hi,
I'm looking for a good design pattern for controlling uniqueness. E.g. I have classes representig a particular database relation. The constructor has the database key(s) as parameter(s). For the other attributes there are corresponding setter and getter methods.
How can I make sure, that I have only one instance with key(s) foo in my system?
Of course I have some ideas but I'm not sure if that is the best thing I could do. So I could use a map, to map the keys to the tuples.
This map could be in another class foo2 which creates the objects of foo1 (which has only a protected or package-private constructor).
Or I could place the map into foo1 itself as a static variable, and add a static factory method. The constructors would then be protected or private. Are these solutions good? Which one to prefer?
How can I handle other unique attributes (not part of the key)?
The equals method for such a class could then test the keys only, since there is only one object with such a key in the system, right?
Thanks for any help.
Greets
Puce

The class could have only private constructors and a public static getter method, which would decide based on some collection of the object created so far, whether to create a new one or give an old one.

Flex design pattern for BlazeDS transfer objects

Dear Community,
I have a question regarding the nature of objects transferd from BlazeDS backend to the Flex client.
According to some adobe docs all the presentation logic should be in flex and BlazeDS should provide only services.
The question is what kind of transfer objects should be used? with what level of abstraction?
To make it more clear let's talk about a simple forum application like adobe forums.
I have created a Forum service, which returns a Forum transfer object, which has a List of Threads, with each thread having a List of Messages.
Flex gets the Forum transfer object and does all the presentaiton work.
This is a very nice seperatin of concerns architecture BUT there are two major performance issues:
- when the forum becomes bigger the transfer object will be huge
- the flex will use huge client resources to create the presentation of the forum transfer object.
So my question is what is your strategy/ design pattern for such a problem.
An obvious answer would be create services that include the presentation logic and use transfor objects like ThreadListPage which will include only the first 10 threads.
Thanks in advance

I think you are going to get a few varied types of answers to a general question like this, but I will comment on a few things. First, you should only be transmitting the data that you need to use or display to the user at the time. If this forum was implemented in Flex (I wish) you wouldn't transfer the text for all the threads. You might not transfer the thread text at all (just the subjects), you'd make calls back to the server to fetch that data when and if you need it.
Also, I think you are overestimating the resources required for the Flex "presentation layer". If you think about it, these workstations we have here are pretty idle most of the time when you're at a website. Nowadays there's plenty of processing power just sitting there waiting, so as long as your design isn't flawed the CPU or memory are rarely going to be a bottleneck with Flex.
The way I design, BlazeDS (or GraniteDS etc) should mostly just be "serving data". There is some flexibility available, for example I don't see a problem with putting certain types of business rules (such as a limit on the number of results that can be recieved in a search) within server side code, and validation rules on the Flex side. So there's not too many "industry standards" in Flex yet beyond maybe what's done in the various standard architectures, at least not that I'm aware of.
You might find it beneficial to look into some of the various frameworks/architectures available like Cairngorm, Mate, Swiz, and so on. Learning how they work (looking at examples) would probably answer some of your questions too.

Design pattern for CLD

What is the best design pattern to pass the CLD?
I think that the "producer/consumer" is not the best way because it need more time..
A simple "state machine" is more fast.
Solved!
Go to Solution.

State Machine with the capability to handle events from the user and timing. That will handle all of the scenarios I have seen.
There are only two ways to tell somebody thanks: Kudos and Marked Solutions
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Design pattern for unprotecting and reprotecting sheets with VBA?

Many macros can't run when a worksheet is protected, so when I develop an Excel workbook that has protected worksheets, I have to unprotect worksheets when macros are called and then reprotect the worksheets once the macro has completed.
The current design pattern I use for this is the following:
I look at each procedure individually and consider which sheets need to be unprotected for it to run. Then in each procedure I write:
Sub Test()
Dim bSheet1Protected as boolean
Dim bSheet2Protected as boolean
bSheet1Protected = Sheet1.ProtectContents
bSheet2Protected = Sheet1.ProtectContents
bSheet1Protected.Unprotect
bSheet2Protected.Unprotect
'''The rest of my code
if bSheet1Protected then Sheet1.Protect
if bSheet2Protected then Sheet2.Protect
End Sub
But I imagine that maybe there are better ways of doing this. What is your preferred design pattern for unprotecting and reprotecting sheets with VBA?

Hi JP3O,
I think it is a good practice to unprotect the worksheet before execute some code and protect it back after the code execute finished.
>>But I imagine that maybe there are better ways of doing this. What is your preferred design pattern for unprotecting and reprotecting sheets with VBA?<<
I am not able to find a better way since we always need to unproect the worksheet if some code didn't not executed successful when the worksheet is proected.
Regards & Fei
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Design Pattern For Web Services.

I tried asking siomilar questions in WebService Forum but didn'y got any replies.
Can anybody tell me what should be the Design for Web Services.
I have understanding that there can be just 1 Interface/Implementation class for each Web Service, and which will have 1 end point.So for evry such Interface we will have to have 1 Web Service.
Can someone please clarify wheather I'm correct or not ?
I guess that If my application has many Interfaces and I have to expose the application as Web Service.Then I will have to expose all methods from one Interface and then expose this new Interface as Web Service.
Is this how WS will work.
Any pointers to design PATTERNS for Web Service will be highly appreciated.
Thanks
Rahul

I don't know if anyone has documented new patterns specifically aimed at web services but the old ones definitely apply. Like you were alluding to, there is a letter-envelope decoupling of interface and implementation with the XML WSDL interface and coded implementation.

Best design pattern for a large number of options?

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