I am new to this tech but I am close to the concept of Channel. I understand that the channel are ledgers within a bigger ledger( i.e. small chain specific to some users only within the entire blockchain). Based on this I have few questions.
Lets say there are retail markets where there is scope for negotiations in rate and hence each vendor can sale same thing to different people with different prices. So assuming that there are 1000 people and 1000 vendors possibly there could be many channels. How these are managed?
I understand that the blockchains are linear data structure (unless two blocks are created simultaneously, there is a word for this but I forgot it), If I have to access previous data for certain user. How efficient it is going to be for such operations? i.e. take an example of bank credit card transactions. If I want to see all my transactions for last 5 months. How efficient it is going to be?
I am not claiming that I am completely correct in my understanding but these things are bugging me.It would be very nice if someone help me clear these?
Thanks :)
Update
I have gone through this link it also talks about something related to my questions in below comments. i.e. related to businesses (questions private blockchain).
I like more the definition of channels as different blockchains using a common network or common parts of a network. It allows privacy and different organisation structures.
Yes, it could have possibly so many channels as vendor-people pair. Of course, it depends on which privacy you want to achieve.
If you want to access previous datas for previous operations, you have the possibility to have a state database running alongside the peers, which are a state representation of the linear structure. You can use LevelDB or CouchDB. CouchDB allows you to use complex rich queries to access your data.
ledger can only exists in channel. And the channel is composed of peers. the peers out of the channel cannot get access to the ledger data.
I am not sure what you mean by "Operation". You can create it and close it(this will be supported in later version) When you need it ,create it and you can close after use.
If the business is independent, you have to create so many channels. you just say vendor can sale same thing to different people with different prices. . each of them will be used for different scenario.
if you want to get access to the previous data, of course you can. But not maybe as efficient as you the bank card now. But this is doable. Now we use sdk to access. maybe later with more development of the sdk, more graphic tool will be developed, enabling it used as easy as possible.
Related
For my internship, I need to implement a blockchain based solution to manage a drug supply chain. The management of this supply chain implies to track-and-trace (geolocate) a drug on the chain, but also to monitor the storage temperature to see if the cold chain is respected. For that I created a mock-up of the POC my Dapps (https://balsamiq.cloud/sum5oq5/p8lsped)and also I wanted to prepare myself by doing a UML and a use cases. However, I didn't find a lot of information about blockchain's UML and use cases besides two literatures which were quite different, so I don't know if what I did was correct or not...
The users of my Dapps will be the following ones:
The stakeholders (Manufacturers, Distributors and Retailers) which will use the Dapps to place orders and also monitor them. They also can search in the historic a specific order. Finally, trough IOT sensors they update the conditions of the order (temperature & location).
The administrator which roles is to update the Dapps and its rules. But also to add or delete user while also defining the rights that they have on the blockchain (I intend to use a permisionned blockchain). Finally, they are also here to help in case of technical problem.
The Dapps that I'm thinking about works in the following:
A user, the customer, can place an order (a list of products) to a
certain seller and choose the final destination of the order.
The order is then put together before being shipped or stocked in the
depots of one of the stakeholders (distributor or retailer) with a
description of the stocking and/or shipping condition of the product
(for example the product must be stocked or transported in a room
with a temperature of less than 5°C). During the shipping and
storing, an IOT device will feed the drops with the temperature and
geolocation of the product by updating the data each 5-10mn.
Obviously they will be a function that allows all the users to see
the history of the order passed and search inside a specific order.
In case where the temperature doesn't respect the temperature
recommended, then the smart-contract send an alert. The same if the
collocation of the product is "weird" like being in some European
countries and not in an Asian country, an alert will be sent again by
the smart-contractual. Finally, in the case where the product is sent
to the asked location by the customer, then the money for the order
will be paid to the seller.
So based on what I explained, I came here in hope that someone tell me if the use cases and UML that I did were correct or not.
I thank in advance anybody who'll take the time to help me.
I am using hyperledger fabric to be able to trace products to check its provenance within a supply chain. This project is meant for a lot of products, especially for longer periods of time.
I am having trouble figuring out what kind of identifiers to use for identifying a product which needs to be transacted in the blockchain. All the data will be stored within it forever.
According to a source (https://www.gs1ca.org/files/How_to_Create_a_GTIN.pdf) I can only make a max amount of 100.000 unique codes per company. After that I am geussing it needs to be reused. What are the identifiers I can use for basically an unlimitted amount of unique-codes within blockchain? Are there standards to handle this? Or should I identify my assets with two identifiers?
In the event a company exhausts their 100,000 GTIN's they can apply for a second, or a third, or so on, GS1 Prefix. So essentially you should map their GTIN's along with their GS1 prefix.
Do some research on IBM FoodTrust, it is the most well known GS1 standard-based system for tracking goods on a Blockchain (Hyperledger).
How can we rotate CUSTOMER NUMBER values in CICS?
For eg. If customer number is c52063
How can i get onto next value ie, c52064(say) in CICS?
This is a very broad question, essentially you're asking what persistence mechanisms are available in CICS.
Please understand there is a big difference between...
what is technically possible
what is allowed in your shop
what is likely to provide a robust and maintainable solution given your requirements
These are three very different things. Some of us answering questions here on StackOverflow have life experiences that make us reticent about answering questions regarding what is technically possible absent any mention of what is allowed in your shop or what the actual business requirement that is being solved.
Mainframes have been around for over half a century, and many shops have standard solutions to technical problems. Sometimes the solution is "don't do that, and here's what we do instead." Working against the recommendations of your technical staff, or your shop standards, is career limiting.
A couple of options, not intended to be an exhaustive list...
SELECT and UPDATE the value in a DBMS (such as DB2). You must code your SELECT SQL with FOR UPDATE.
READ and REWRITE the value in a VSAM file. You must code your READ with the UPDATE option.
In either case you are holding a lock on the resource until you hit either an explicit (EXEC CICS SYNCPOINT) or implicit (end of transaction) syncpoint or rollback (EXEC CICS SYNCPOINT ROLLBACK or abend condition). Holding such a lock means all other instances of your transaction will wait until the syncpoint or rollback has occurred.
If you know for certain your application will be limited to a single CICS region... Other options would include having a transaction initiated as part of region initialization processing that would obtain and populate a shared resource such as a temporary storage queue with a name known to your application with the last known customer number. This initialization transaction would have to obtain the highest used customer number from somewhere, probably a DBMS or a VSAM file. Applications would have to be coded to ENQ and DEQ their access to the temporary storage queue. You could do this without using a temporary storage queue but with shared memory and storing the address of that memory in the CICS CWA for your region. Again, ENQ and DEQ logic would have to be coded in the applications.
You could use a named counter as defined by your CICS Systems Programmer. Be certain to read and understand the recovery requirements for your application as documented in the IBM Knowledge Center.
Again, this is not an exhaustive list, it is just to give an overview of some of the options available. Talk to your technical staff, they likely have either a standard solution as employed by your shop or a preference based on their experience and your requirements.
I am working on DDD project and I am currently focused on two bouned contexts, Orders and Warehouse.
What confuses me is the following situation:
Order keep track of all the placed orders, and warehouse keeps track about all the available inventory. If user places one order for certain product item, that would mean one less item of that product in a warehouse. I am oversimplifying this process, so please bear with me.
Since two domain models are placed inside of a different BC, i am currently relying on eventual consistency ie. after one item has been sold, it would eventually be removed from the warehouse.
That situation unfortunately leads to the problem scenario where another user could simultaneously make another order of the same item, and it would appear as available until eventual consistency kicks is. That is something it is unacceptable by the domain expert.
So IMO I am stuck with two options
merge order and warehouse (at least the part regarding product
inventory, units available in warehouse) into one BC
have Order BC (or microservice if you wish) to be dependent of Warehouse BC (microservice) in order to pull a live product units
available
Which option does actually follows DDD patern? Is there another way out?
You could use a reservation system with a timeout.
Using a messaging analogy: With a broker-style queuing mechanism (such as RabbitMQ) you get a message from the queue and you have control over it until you either acknowledge that it can be removed from the queue or you release it back to the queue.
You could do the same thing in your ordering process. You reserve any items on your order. SO when you add them they have a status of, say, reserving and upon sending some message to reserve the items. If the response comes back you can decide how to proceed. Perhaps you could add any items that cannot be reserved onto a back order or try again later.
There are going to be different ways to approach this. Depending on your business case it may be acceptable to only check availability when someone really accepts the order.
If you domain expert reckons it is totally unacceptable that having this resolved at the end of the process then you could move it to the start. The issue is of course that user A could reserve and never buy thereby losing user B as a customer; whereas only applying the real "taking" of the item at the end of the process is closer to ensuring a purchase. But that is a business decision.
This issue is a really great example of where reality actually is eventually consistent. Is it really the best thing to decline an order if there is no inventory currently in the warehouse - even if there was a replenishment due in the next 20 minutes?
What if the item was actually on the shelf, but the operator hadn't yet keyed it into the system?
Sometimes designers and domain experts assume that people want 100% consistency, when really, users might be willing to accept a delay in confirmation of their order, if it increased the chance that their order would be accepted rather than rejected.
In the case above, why make it the user's job to retry their order N minutes later? In an eventually consistent system, you can accommodate such timing flexibility by including a timeout to retry the attempt to fulfill the order for a period of time before confirming to the client that it really wasn't possible.
There are technical solutions that will give you 100% consistency, but I think really this is not a technical challenge but a cultural/mindset one, changing people's minds about what is possible & acceptable to achieve an what is actually a better outcome.
IMO you can build a PlaceOrderSaga which will ask for inventory availability before placing the order.
I'm getting familiar with DHT and I mostly understand how it works. However, I don't quite understand what happens if you want to have separate DHTs with different entry types in each. Is this possible?
If I use a popular DHT library, does that mean I put and get entries using the same DHT as every user of said library? Or is DHT universal for everyone? How do you define an owner of a DHT, or how do you define a separate, contained DHT?
Yes, you can make separate DHTs. However you need to make the 'on the wire' protocols slightly diffrent so they can't speak to each other and get mixed up.
You can actually have unlimited numbers of DHTs using the same protocol as long as peers don't know each other.
This is the important part when you set up a network. You have to know a second peer to intitially create the network. The next peer would have to know one of the two initial nodes, the next one needs knowledge of one of the three above and so forth.
You are also able to be connected to multiple DHTs on the same host without the two interferring (at least in terms of data exchange, not in terms of local ressources). And you are also able to joins those two DHTs by telling one of them about the peers you are connected to in the other DHT. Though that might be not as easy as it sounds.