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I'm actually developping a system for bus ticket reservation. The provider has many routes and different trips. I've setup a rather comprehensive database that maps all this together, but i'm having trouble getting the pathing algorithm working when i comes to cross route reservation.
For example, the user wants to go from Montreal to Sherbrooke, he'll only take what we call here Route #47. But in the event he goes to Sutton instead of Sherbrooke, he now has to transfer into route #53 at some point.
Now, it isn't too hard to detect one and only one transfer. But when i comes to detecting what are the options he can do to cross multiple routes, i'm kinda scared. I've devised a cute and relatively efficient way to do so on 1-3 hops using only SQL but i'm wondering how i should organize all this in a much broader spectrum as the client will probably not stay with 2 routes for the rest of is life.
Example of what i've thought of so far:
StartingStop
joins to Route
joins to StopsOfTheRoute
joins to TransfersOnThatStop
joins to TargetStopOfThatTransfer
joins to RouteOfThatStop
joins to StopsOfThatNewRoute
[wash rince repeat for more hops]
where StopsOFThatNewRoute = EndingStop
Problem is, if i have more than 3 hops, i'm sure my SQL server will choke rather fast under the pressure, even if i correctly index my database, i can easily predict a major failure eventually...
Thank you
My understanding of your problem: You are looking for an algorithm that will help you identify a suitable path (covering segments of one or more routes).
This is as Jason correctly points out, a pathfinding problem. For this kind of problem, you should probably start by having a look at Wikipedia's article on pathfinding, and then dig into the details of Djikstra's algorithm. That will probably get you started.
You will however most likely soon realise that your data model might pose a problem, both from a structure and performance perspective. Typical example would be if you need to manage time constraints: which path has the shortest travel time, assuming you find several? One path might be shortest, but only provide one ride per day, while another path might be longer but provide several rides per day.
A possible way of handling this is to create a graph where each node corresponds to a particular stop, at a particular time. An edge would connect from this stop in room-time to both other geographical stops, as well as itself at the next point in time.
My suggestion would be to start by reading up on the pathfinding algorithms, then revisit your data model with regards to any constraints you might have. Then, focus on the structure for storing the data, and the structure for seaching for paths.
Suggestion (not efficient, but could work if you have a sufficient amount of RAM to spare). Use the relational database server for storing the basics: stops, which routes are connected to which stops and so on. Seems you have this covered already. Then build an in-memory representation of a graph given the constraints that you have. You could probably build your own library for this pretty fast (I am not aware of any such libraries for PHP).
Another alternative could be to use a graph database such as Neo4j and its REST interface. I guess this will require significant some redesign of your application.
Hope this gives you some helpful pointers.
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Currently, I am working on a website and just started studying backend. I wonder why nobody uses JSON as a database. Also, I don't quite get the utility of php and SQL. Since I could easily get data from JSON file and use it, why do I need php and SQL?
ok! let assume you put the data in a JSON variable and store it in a file for all your projects.
obviously, u need to add a subsystem for getting back up, then you will write it.
you must increase the performance for handling a very large amount of data, just like indexing, hash algorithms, and... , assume u handle it.
if you need some API for working and connecting with a variety of programming languages, u need to write them.
what about functionalities? what if you need to add some triggers, store procedures, views, full-text search and etc? ok, you will pay your time and add them.
ok, good job, but your system will grow up and you need to scale it, can you do it? u will write abilities for clustering across servers, sharding, and ...
now you need to guarantee that your system will compatible with ACID rules, to keep atomicity, Consistency, Isolation, and Durability.
can you always handle all querying techniques (Map/Reduce) and respond with a fast and standard structure?
now it's time to offer very quick write speeds, it brings serious issues for you
ok, now proper your solutions for condition racing, isolation level, locking, relations and ...
after you do all this work plus thousands of many others, probably you will have a DBMS a little bit just like MongoDB or other relational and non-relational databases!
so it's better to use them, however, obviously, you can choose to don't to use them too, I admit that sometimes saving data in a single file has better performance, but only sometimes, in some cases, with some data, for some purpose! if you know what exactly you do, then ist OK to save data in a JSON file.
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I finished creating an accounting web application for an organization using codeignter and mysql db, and I have just submitted it to them, they liked the work, but they asked me how they would transfer their old manual data to the new one online, so that their members would be able to see their account balances and contributions history.
This is a major problem for me because most of my tables make use of 'referential integrity' to ensure data synchronization and would not support the style of their manual accounting.
I know a lot of people here have faced cases like this and I would love to know the best way to collect users history, and I also know this might probably be flagged as not a real question, but I really really have to ask people with experience.
I would appreciate all answers. Thanks (And vote downs too)..
No matter what the case is, data conversions are very challenging and almost always time consuming. Depending on the consistency of the data in question, it could be a case that about 80% of the data will transfer over neatly if you create a conversion program using PHP. That conversion code in and of itself may be more time consuming than it is worth. If you are talking hundreds of thousands of records and beyond, it is probably a good idea to make that conversion program work. Anyone who might suggest there is a silver bullet is certainly not correct.
Here are a couple of suggested steps:
(Optional) Export your Excel spreadsheets to Access. Access can help you to standardize data and has tools in place to help you locate records which have failed in some way. You can also create filters in Access if you need to. The benefit of taking this step, if you are familiar with Access, is that you have already begun the conversion process to a database. As a matter of fact, if you so desire, you can import your MySQL database information into Access as well. The benefit of this is pretty obvious: You can create a query and merge your two separate tables together to form one table, which could save you a great deal of coding.
Export your Access table/query into a CSV file (note, if you find it is overkill or if you don't have Access, you can skip step 1 and simply save your .xls or .xlsx file to type .csv. This may require more legwork for your PHP conversion code but that is probably a matter of preference. Some people prefer to avoid Access as much as possible, and if you don't normally use it you will be wasting time trying to learn it just to save yourself a little bit of time).
Utilize PHP's built-in str_getcsv function. This will convert a CSV file into a PHP array.
Create your automated program to parse through each record. Based on the column and its requirements, you can either accept or reject records. You can then export your data, such as was done in this SO answer, back to CSV. You can save two different CSV files, one with accepted records, and one with rejected records.
With rejected records, which are all but inevitable when transferring from a spreadsheet, you will need to have a course of action. The simplest way for your clients is probably to give them a procedure to either manually import records into the database, if you've given them an interface to do so, or - probably simpler but requiring more back-and-forth - to update the records in Excel to be compliant with the new system.
Edit
Based on the thread under your question which sheds more light on what you are trying to do (i.e., have a parent for each transaction that is an accepted loan), you should be able to contrive a parent field, even if it is not complete, by creating a parent record for each set of transactions based around an account. You can do this via Access, PHP, or, more likely, a combination.
Conclusion
Long story short, data conversions take time. If you put the time in up front, it will be far easier to maintain a standardized series of information in the long run. If you find something which takes less time in the beginning, it will mean additional work for you in the long run in order to make this "simple" fix work over time.
Similarly, the closer you can get legacy data to conform to your new data, the easier it will be for your clients to perform queries etc. While this may mean that some manual entry will be required on the part of you or your client, it is better to inform the client of the pros and cons of each method fully and let them decide. My recommendation would always be to put extra work in at the front-end because it almost always ends up cheaper than having to deal with a quick fix in the long run, but that is not always practical given real world constraints.
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I recently got an internship involving the writing of an sql database and don't really know where to start.
The database will hold the information of a ton of electrical products: including but not limited to watt usage, brand, year, color, size, country of origin. The database's main task is to use some formulas using the above information to output several energy-related things. I will also be building a simple gui for it. The database will be accessed solely on Windows computers by no more than 100 people, possibly around the area of 20.
The organization does not normally give internships, and especially not to programmers (they're all basically electrical engineers); I got it via really insisting to a relative that works there who was looking into how to organize some of the products they overlook. In other words, I can't really ask THEM for guidance on the matter since they're not programmers, which is the reason I headed here to get a feel of where I'm starting.
I digress -- my main concerns are:
What is some recommended reading or viewing for this? Tips, tricks?
How do I set up a server for this? What hardware/bandwidth/etc. do I require?
How do I set up the Database?
For the gui client, I decided to take a look at having it be a window showing a webpage built with the sql embeded into php. Is this a good idea? Recommended reading for doing that? What are alternatives?
What security measures would you recommend? Recommended reading?
I have: several versions of Microsoft's mySQL servers, classroom experience with mySQl and PHP, several versions of Visual Studio, access to old PCs for testing (up to and including switching operating systems, hardware, etc.), access to a fairly powerful PC (non-modifiable), unlimited bandwidth.
Any help would be appreciated, thanks guys!
What is some recommended reading or viewing for this? Tips, tricks?
I'd recommend spending quite a bit of time in the design stage, before you even touch a computer. Just grab some scrap paper and a pencil and start sketching out various "screens" that your UI might expose at various stages (from menus to inputs and outputs); show them to your target users and see if your understanding of the application fits with the functionality they expect/require; consider when, where, how and why they will access and use the application; refine your design.
You will then have a (vague) functional specification, from which you will be able to answer some of the further questions posed below so that you can start researching and identifying the technical specification: at this stage you may settle upon a particular architecture (web-based?), or certain tools and technologies (PHP and MySQL?). You can then identify further resources (tutorials?) to help progress toward implementation.
How do I set up a server for this? What hardware/bandwidth/etc. do I require?
Other than the number of users, your post gives very little indication of likely server load from which this question can be answered.
How much data will the database store ("a ton of electrical products" is pretty vague)? What operations will need to be performed ("use some formulas ... to output several energy-related things"
is pretty vague)? What different classes of user will there be and what activities will they perform? How often will those activities write data to and read data from the database (e.g. write 10KiB, once a month; and read 10GiB, thousands of times per second)? Whilst you anticipate 20 users, will they all be active simultaneously, or will there typically only be one or two at any given time? How critical is the application (in terms of the reliability/performance required)?
Perhaps, for now, just install MySQL and see how you fare?
How do I set up the Database?
As in, how should you design the schema? This will depend upon the operations that you intend to perform. However, a good starting point might be a table of products:
CREATE TABLE products (
product_id SERIAL,
power INT UNSIGNED COMMENT 'watt usage',
brand VARCHAR(255),
year INT UNSIGNED,
color VARCHAR(15),
size INT UNSIGNED,
origin CHAR(2) COMMENT 'ISO 3166-1 country code'
);
Depending upon your requirements, you may then wish to create further tables and establish relationships between them.
For the gui client, I decided to take a look at having it be a window showing a webpage built with the sql embeded into php. Is this a good idea? Recommended reading for doing that? What are alternatives?
A web-based PHP application is certainly one option, for which you will find a ton of helpful free resources (tutorials, tools, libraries, frameworks, etc.) online. It also is highly portable (as virtually every device has a browser which will be able to interact with your application, albeit that ensuring smooth cross-browser compatibility and good cross-device user experience can be a bit painful).
There are countless alternatives, using virtually any/every combination of languages, runtime environments and architectures that you could care to mention: from Java servlets to native Windows applications, from iOS apps to everything in between, the choice is limitless. However, the best advice is probably to stick to that with which you are already most comfortable/familiar (provided that it can meet the functional requirements of the application).
What security measures would you recommend? Recommended reading?
This is another pretty open-ended question. If you are developing a web-app, I'd at very least make yourself aware of (how to defend against) SQL injection, XSS attacks and techniques for managing user account security. Each of these areas alone are quite large topics—and that's before one even begins to consider the security of the hosting platform or physical environment.
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We're taking our functional web-based software that's previously been exclusive to our business and introducing licensing options so that other businesses may use it.
What considerations should be taken into account when choosing between the two approaches:
Modify the code to permit multiple users
Install multiple instances of the code; one for each new user. E.G. completely duplicated, separate databases & PHP.
The software is PHP-based. We intend to offer multiple packages. Server load grows quadratically with increased use per license, due to large amounts of processing that occurs through scheduled cron jobs.
Update: despite the only answer suggesting we should not do this, we are still leaning toward modifying the code to permit multiple users. Does anyone else have any input?
Update 2: for the security reasons, we again changing our position to the multiple-instances solution.
Having done this myself in the last several months, My advice is don't do what we did, which is modify the code to permit multiple users. Turns out that's a rabbit hole and will introduce:
code complexity (adding new simple features will often become difficult)
bugs (due to increased complexity)
security problems (a huge amount of time was spent ensuring clients cannot access each other's data)
performance issues (tables with ~5,000 rows will suddenly grow to ~5,000,000 rows. Performance issues that weren't even noticeable suddenly created ~20 second page load times)
If we could do it again our approach would be something like:
Put each client on a subdomain (maybe even allow them to supply their own full domain name), allowing you to have a separate apache virtual host for each one. Buying a license to something like cPanel is worth serious consideration, and investigate how to automate or semi-automate creating new accounts.
Have a separate database for each client. Each with a different database password. This will provide excellent security and excellent performance (all the databases (and their tables) will be small).
It's up to you whether the actual php source code should be shared between all of these clients, or have a separate copy for each one. A global directory for the files is perfectly reasonable, and will make updates easy, while a separate copy will make customisations easier. Perhaps a hybrid is the right approach here.
One day we might even end up tearing out most of the work done in the last six months, to start again with this approach.
At first glance it seems like this will increase server load, but in reality if you have enough clients for load to even be a consideration, then you will want to be able to spread clients across multiple servers. And that's a piece of cake if it's well segregated.
Need some ideas/help on best way to approach a new data system design. Basically, the way this will work is there will be a bunch of different database/tables that will need to be updated on a regular (daily/weekly/monthly) basis with new records.
The people that will be imputing the data will be proficient in excel. The input process will be done via a simple upload form. Then the system needs to add what was imported to the existing data in the databases. There needs to be a "rollback" process that'll reset the database to any day within the last week.
There will be approximatively 30 to 50 different data sources. the main primary interface will be an online search area area. so all of the records need to be indexed/searchable.
Ideas/thoughts on how to best approach this? It needs to be built mostly out of php/mysql.
imputing the data
Typo?
What you are asking takes people with several years formal training to do. Conventionally, the approach would be to draw up a set of requirements, then a set of formal specifications, then the architecture of the system would be designed, then the data design, then the code implementation. There are other approaches which tend to shortcut this. However even in the case of a single table (although it does not necessarily follow that one "simple upload form" corresponds to one table), with a single developer there's a couple of days work before any part of the design could be finalised, the majority of which is finding out what the system is supposed to do. But you've given no indication of the usage nor data complexity of the system.
Also what do you mean by upload? That implies they'll be manipulating the data elsewhere and uploading files rather than inputting values directly.
You can't adequately describe the functionality of a complete system in a 9 line SO post.
You're unlikely to find people here to do your work for free.
You're not going to get the information you're asking for in a S.O. answer.
You seem to be struggling to use the right language to describe the facts you know.
Your question is very vague.