I would like to create a registry of the times a user has viewed audio visual content. I created the following diagram and was wondering if it would be a good way to achieve it.
Note: The AudiovisualContent is connected to DateTimeStamp just as a way to record when it was added to the platform.
Is the diagram correct and is it meaningful?
The diagram seems formally correct and has the advantage of being very clear on multiplicity and role names for the DateTimeStamp.
It is diffucult to say if this approach is correct for a "registry". But it makes sense at first sight; I understand from the diagram that:
a Profile (user?) can do several Viewing and each Viewing is about one Audiovisual Content. Conversely, an Audiovisual Content can be the subject of several Viewing, and each Viewing is performed by a Profile
Each Viewing (of a given content by a given user) has a DateTimeStamp
Each Audiovisual Content has a DateTimeStamp corresponding to the moment the content was added.
If a user views the same content several time at different moments, each of this Viewing may have a different rating, and the rating is optional.
What I can further infer from the multiplicities, is that the timestamp corresponds to the beginning of the viewing act (because if it would be the end of the viewing, there wouldn't be timestamp when the viewing starts, so the multiplicity would have been 0..1).
Areas of concern
The DateTimeStamp is a class according to your diagram. The fact that you have a 1 multiplicity on the side of the Viewing and on the side of Audiovisual Content means that every single timestamp must be associated with BOTH. I doubt that this is correct.
You could consider using 0..1 instead, which would leave the possibility of having a time stamp associated with only one of the two or none at all. But still the timestamp could possibly have both, with the risk of inconsistency between them.
Personanlly, I'd go for * to clarify that many viewing and uploading could happen at the same time. I'd probably show it as a property -addedOn: DateTimeStamp and -viewedOn:DateTimeStamp.
In reality, the time stamp is very probably a value object. You could then consider making it a «dataType»; showing it as a property may then seem even more intuitive.
Unrelated: while your current way of modeling Viewing as a class is perfectly fine, you may be interested to show is as an association class between many Profile and many Audiovisual Content
Related
I have an Entity Storm, which has two One-to-Many relationships, "history" and "forecast" both of these are NSSets that contain a StormPosition Entity which contains time, latitude and longitude.
I am able to build this but while I can set up the "history" and "forecast" relationship, they can't seem to both point to objects of type StormPosition because the inverse relationships can't both point back to the Storm Entity.
I assume this is because when I do:
myStormPosition.owner = self
it needs to know which NSSet (history or forecast) to place it into.
Do I need to mix these into one "track" relationship? I'd rather not since it is nice to have one set for history and one set for forecast without having to examine the date property.
Also, elsewhere in the program I'd like to be able to only work with a StormPosition type instead of a HistoricPosition and PredictedPosition type which would effectively be the same but make for difficult type casting unless I gave them both a parent class that was identical.
This does feel to me like one of the rare occasions when you would benefit from using a parent entity/class. Be careful with this, because all instances of both HistoricPosition and PredictedPosition will have eat space in the persistent store for all of properties of both (because they have a common parent).
Will you have multiple Forecasts per storm? E.g. predicted track as of day 1, predicted track as of day 2, …?
It does feel like a heavyweight solution, though. Perhaps a protocol to include the location and timestamp? Get away fromthe notion of a Position entity completely? A forecast position has a valid time, and the time it was issued, while a historic track position has only the time it was recorded.
I want to sanity check myself on a view projection, in regards to if an intermediary concept can purely exist in the read model while providing a bridge between commands.
Let me use a contrived example to explain.
We place an order which raises an OrderPlaced event. The workflow then involves generating a picking slip, which is used to prepare a shipment.
A picking slip can be generated from an order (or group of orders) without any additional information being supplied from any external source or user. Is it acceptable then that the picking slip can be represented purely as a read model?
So:
PlaceOrderCommand -> OrderPlacedEvent
OrderPlacedEvent -> PickingSlipView
The warehouse manager can then view a picking slip, select the lines they would like to ship, and then perform a PrepareShipment command. A ShipmentPrepared event will then update the original order, and remove the relevant lines from the PickingSlipView.
I know it's a toy example, but I have a conceptually similar use case where a colleague believes the PickingSlip should be a domain entity/aggregate in its own right, as it's conceptually different to order. So you have PlaceOrder, GeneratePickingSlip, and PrepareShipment commands.
The GeneratePickingSlip command however simply takes an order number (identifier), transforms the order data into a picking slip entity, and persists the entity. You can't modify or remove a picking slip or perform any action on it, apart from using it to prepare a shipment.
This feels like introducing unnecessary overhead on the write model, for what is ultimately just a transformation of existing information to enable another command.
So (and without delving deeply into the problem space of warehouses and shipping)...
Is what I'm proposing a legitimate use case for a read model?
Acting as an intermediary between two commands, via transformation of some data into a different view. Or, as my colleague proposes, should every concept be represented in the write model in all cases?
I feel my approach is simpler, and avoiding unneeded complexity, but I'm new to CQRS and so perhaps missing something.
Edit - Alternative Example
Providing another example to explore:
We have a book of record for categories, where each record is information about products and their location. The book of record is populated by an external system, and contains SKU numbers, mapped to available locations:
Book of Record (Electronics)
SKU# Location1 Location2 Location3 ... Location 10
XXXX Introduce Remove Introduce ... N/A
YYYY N/A Introduce Introduce ... Remove
Each book of record is an entity, and each line is a value object.
The book of record is used to generate different Tasks (which are grouped in a TaskPlan to be assigned to a person). The plan may only cover a subset of locations.
There are different types of Tasks: One TaskPlan is for the individual who is on a location to add or remove stock from shelves. Call this an AllocateStock task. Another type of Task exists for a regional supervisor managing multiple locations, to check that shelving is properly following store guidelines, say CheckDisplay task. For allocating stock, we are interested in both introduced and removed SKUs. For checking the displays, we're only interested in newly Introduced SKUs, etc.
We are exploring two options:
Option 1
The person creating the tasks has a View (read model) that allows them to select Book of Records. Say they select Electronics and Fashion. They then select one or more locations. They could then submit a command like:
GenerateCheckDisplayTasks(TaskPlanId, List<BookOfRecordId>, List<Locations>)
The commands would then orchestrate going through the records, filtering out locations we don't need, processing only the 'Introduced' items, and creating the corresponding CheckDisplayTasks for each SKU in the TaskPlan.
Option 2
The other option is to shift the filtering to the read model before generating the tasks.
When a book of record is added a view model for each type of task is maintained. The data might be transposed, and would only include relevant info. ie. the CheckDisplayScopeView might project the book of record to:
Category SKU Location
Electronics (BookOfRecordId) XXXX Location1
Electronics (BookOfRecordId) XXXX Location3
Electronics (BookOfRecordId) YYYY Location2
Electronics (BookOfRecordId) YYYY Location3
Fashion (BookOfRecordId) ... ... etc
When generating tasks, the view enables the user to select the category and locations they want to generate the tasks for. Perhaps they select the Electronics category and Location 1 and 3.
The command is now:
GenerateCheckDisplayTasks(TaskPlanId, List<BookOfRecordId, SKU, Location>)
Where the command now no longer is responsible for the logic needed to filter out the locations, the Removed and N/A items, etc.
So the command for the first option just submits the ID of the entity that is being converted to tasks, along with the filter options, and does all the work internally, likely utilizing domain services.
The second option offloads the filtering aspect to the view model, and now the command submits values that will generate the tasks.
Note: In terms of the guidance that Aggregates shouldn't appear out of thin air, the Task Plan aggregate will create the Tasks.
I'm trying to determine if option 2 is pushing too much responsibility onto the read model, or whether this filtering behavior is more applicable there.
Sorry, I attempted to use the PickingSlip example as I thought it would be a more recognizable problem space, but realize now that there are connotations that go along with the concept that may have muddied the waters.
The answer to your question, in my opinion, very much depends on how you design your domain, not how you implement CQRS. The way you present it, it seems that all these operations and aggregates are in the same Bounded Context but at first glance, I would think that there are 3 (naming is difficult!):
Order Management or Sales, where orders are placed
Warehouse Operations, where goods are packaged to be shipped
Shipments, where packages are put in trucks and leave
When an Order is Placed in Order Management, Warehouse reacts and starts the Packaging workflow. At this point, Warehouse should have all the data required to perform its logic, without needing the Order anymore.
The warehouse manager can then view a picking slip, select the lines they would like to ship, and then perform a PrepareShipment command.
To me, this clearly indicates the need for an aggregate that will ensure the invariants are respected. You cannot select items not present in the picking slip, you cannot select more items than the quantities specified, you cannot select items that have already been packaged in a previous package and so on.
A ShipmentPrepared event will then update the original order, and remove the relevant lines from the PickingSlipView.
I don't understand why you would modify the original order. Also, removing lines from a view is not a safe operation per se. You want to guarantee that concurrency doesn't cause a single item to be placed in multiple packages, for example. You guarantee that using an aggregate that contains all the items, generates the packaging instructions, and marks the items of each package safely and transactionally.
Acting as an intermediary between two commands
Aggregates execute the commands, they are not in between.
Viewing it from another angle, an indication that you need that aggregate is that the PrepareShippingCommand needs to create an aggregate (Shipping), and according to Udi Dahan, you should not create aggregate roots (out of thin air). Instead, other aggregate roots create them. So, it seems fair to say that there needs to be some aggregate, which ensures that the policies to create shippings are applied.
As a final note, domain design is difficult and you need to know the domain very well, so it is very likely that my proposed solution is not correct, but I hope the considerations I made on each step are helpful to you to come up with the right solution.
UPDATE after question update
I read a couple of times the updated question and updated several times my answer, but ended up every time with answers very specific to your example again and I'm most likely missing a lot of details to actually be helpful (I'd be happy to discuss it on another channel though). Therefore, I want to go back to the first sentence of your question to add an important comment that I missed:
an intermediary concept can purely exist in the read model, while providing a bridge between commands.
In my opinion, read models are disposable. They are not a single source of truth. They are a representation of the data to easily fulfil the current query needs. When these query needs change, old read models are deleted and new ones are created based on the data from the write models.
So, only based on this, I would recommend to not prepare a read model to facilitate your commands operations.
I think that your solution is here:
When a book of record is added a view model for each type of task is maintained. The data might be transposed, and would only include relevant info.
If I understand it correctly, what you should do here is not create view model, but create an Aggregate (or multiple). Then this aggregate can receive the commands, apply the business rules and mutate the state. So, instead of having a domain service reading data from "clever" read models and putting it all together, you have an aggregate which encapsulates the data it needs and the business logic.
I hope it makes sense. It's a broad topic and we could talk about it for hours probably.
I am new to KofaxTotalAgility solution, but i am well aware of OCR, OMR and recognition mechanism.
I have two forms in one folder, A and B.
both of them are identical, but due to manual scan there are slight axes change, say 20 pixel right shift, so Layout is slightly differ.
Layout of Image A and Image B are different, position of a form in a page are not fix.
I know, other solution like "abbyy fine reader", provide flexilayout where we can handle this by finding the text and setting up right left top down to automatically identify zones.
As i have started learning KofaxTotalAgility, i am unaware of all option provided by "kofax Transformation Designer".
My question is which Locator should i use, i am currently using/working-on advance zone locator and for one document(Image A) which i set as a reference, extraction is proper. But for other,(Image B) due to layout mismatch text/box field are not getting extracted.
Can anyone point out the right direction from where i can get this case handled properly.
I know, i am asking direct option/solution, any help is highly appreciable.
In general, Kofax Transformations has two groups of locators:
Deterministic. You tell the locator precisely what to do, and how to do it (similar to an imperative approach when programming)
Probabilistic. You just tell your locator what to extract, and it works out the rest (based on AI).
Here's a (non-exhaustive) diagram I created the other day:
When working with forms, you might be tempted to rely on forms-specific locators such as the Advanced Zone Locator. While this locator can account for fields "moving around", for example due to images being jolted, zoomed, or distorted, there are certain limitations. Other locators don't have these limitations - the format locator for example allows you to define a certain pattern (a Regular Expression) that should be matched along with a keyword that has to be found somewhere around that pattern.
For your example, you could create a regex like M|F|X, and then define "Gender" as the keyword that needs to be present on the left.
However, any locator that's ruled by determinism follows Murphy's law - at some point that keyword might change. There could be different languages. And maybe additional letters for certain genders might be added; ultimately breaking your extraction logic.
Enter AI - while Murphy's law still applies when using Group Locators, the difference here is that users can train the system to pick up the new data. Said locator will automatically work out the best way to extract that piece of data. If you used a format locator, the customer would need to get back to you to add additional expressions, or have the keywords changed.
In your particular case, I'd try to use a Trainable Group Locator first. If you already know what you're looking for - for example SSNs that you have somewhere in a database, go for the Database Locator. Use Format Locators as a last resort, as tempting as they may be. Advanced Zone Locators are useful when you deal with forms, but I find myself using them almost exclusively for handprint or checkbox recognition.
I'm creating a Book store in Magento and am having trouble figuring out the best way to handle the Authors of a Book (which would be the product).
What I currently have is an Attribute called "authors" which is multi-select and a thousand [test] values. It's still manageable but does get a little slow when editing a product. Also, when adding an option/value to the authors attribute itself, a huge list is rendered in the HTML making this an inefficient solution.
Is there another approach I should take?
Is it possible to create an Author object (entity type?) which is associated to a product through a join table? If yes, can someone give me an explanation about how that is done or point me to some good documentation?
If I'd take the Author object approach, could that still be used in the layered navigation?
How would I show the list of all books for a single author?
Thanks in advance!
PS: I am aware of extensions like Improved Navigation but AFAIK it adds something like attributes to attributes themselves which is not what I'm looking for.
For Googlers: The same would apply for Artists of a music site or manufacturers.
If you create an author entity type, you'll just increase your work trying to add it to layered navigation, and I don't see a reason why it would be faster.
Your approach seems the best fit to the problem, given the way Magento is set up. How are you going to display 1,000 (which presumably pales in comparison to the actual list) authors in layered navigation?
Depending on the requirements, you could go the route of denormalizing the field and accepting text for it. That would still allow you to display it, search based on it, etc, but would eliminate the need to render every possible artist to manipulate the list. You could add a little code around selecting the proper artist (basically add an AJAX autocomplete to the backend field) to minimize typos as well.
Alternatively, you could write a simple utility to add a new artist to the system without some of the overhead of Magento's loading the list. To be honest, though, it seems that the lag that this has the potential to create on the frontend will probably outweigh the backend trouble.
Hope that helps!
Thanks,
Joe
I'm working on a pretty basic web app (not much more than CRUD stuff). However, the requirements call for a bunch of data to be displayed with each item in the search results - IDs, dates, email addresses, long descriptions... too much to fit neatly into a simple grid, and too dissimilar to make them flow together (like the natural language example from this article.)
Is there a design pattern for attractively displaying many descriptive fields with each search result?
(Please don't tell me to just remove some fields from the results; that's not an option for this project.)
Obviously there are many ways you can handle this, and to a degree it's a factor of your information design abilities and preferences.
Natural Data Groupings
What I would do is try to organize your data into a small number of "buckets." You state that the data are too dissimilar to be arranged into a sentence, but it's likely you can create a few logical groups. Since we can't see all your data, I'll guess that you have information about a person (email, name, ID?), about some sort of event (dates? type?), or maybe about some kind of object related to the person (orders? classes?). Whatever they are, some of the data will be more closely related to each other than others.
Designing in Chunks
Take each loose "bucket" and design a kind of "plate" -- a grouping just for the information in that bucket. The design problem within this constrained chunk is easier to tackle: maybe it's a little table-like layout, maybe it's something non-tabular, like the stackoverflow user "nameplate". Maybe long textual data have their own plates, or maybe they're grouped into a single plate, but with a preview/detail click-for-more arrangement.
Using a Grid
Now that you have a small number of "plates," go back to a grid-like approach for your overall search result row design. Arrange the plates as units within the row, and be sure to keep them aligned. Following an overall grid (HTML table or otherwise) for the plates will avoid an "information soup" problem. You'll have clean columns that scan well, and a readable, natural information hierarchy. The natural language example you cite would indeed be difficult to parse if it were one of many rows displayed in a search results grid.
Consistency
Be sure to use a common "design vocabulary" when you're working on the chunks -- consistent styling of labels, consistent spacing... so when everything's displayed, despite the bulk of information, it all feels like it's part of the same family.
It's an interesting design exercise. Many comps, lots of iteration, and some brainstorming should get you where you need to be.
It probably depends on the content you're displaying. Look at the StackOverflow layout for this question. It has Votes, Title, Description, Tags, Author, etc. The content wouldn't work well in a grid for sure, nor does it flow nicely on it's own.
I think it's time to get creative ;)
No one ever thinks about what this is going to look like on their screen, do they?
One thing you can do is truncate the displayed text, and then display the expanded version in a tooltip on hover, or after the user clicks on it.
For example, display only the two-letter state abbreviation but show the full state name on hover.
Or, to save even more space, only display the state abbreviation, and put the entire address in the tooltip.
For long descriptions, you can display only the first few characters, followed by an ellipsis or the word "More". Then, show the full text either on hover or on click.
One disadvantage of the hover approach is that you can't sort the column on that text. There's nothing for the user to click to request the sort.