html – Where is Business Analyst in the UX / UI Technology Flow

BAs do not fit into UX / UI technology flow but in basic software development flow.
Some of the main functions of the BA are to understand the requirements and then to design the logical architecture of a solution.
These two tasks are closely related to UX / UI and have an impact on UX.

understand the requirements

We read "Know Thy User" everywhere in the UX copy. Well, the BA is the one that is well placed to research the needs of the user. The BA is on the border of both worlds, computer scientists and normal people.
Another UX mantra is the need for user research, not ex post user testing, but the collection of information upstream. This is also what the BA does.
Depending on the status of the cascade or the agility of the business process, the BA would collect and record detailed information, or have a general idea and deepen the details of the first parties to deal with .

imagine a solution

Whenever the BA has collected enough information, it will be able to apply the first use rule of Jakob Nielsen.
It means applying one's professional knowledge to design a set of logical computer constructs that might not do exactly what users are asking for, but perhaps solve their needs sideways.
Alan Cooper brilliantly explains it in this 6 "video.
In short, it is up to BA to design the solution. Not programmers, visual designers, it does not matter: the BA with the PO (Product Owner) and if possible far from the requirements of marketing (in the end, nothing is better than something with a remarkably good user interface).

What does the BA do?

As stated in the previous answers, the BA writes.
Depending on the culture of the company, she can write user stories, use cases or laundry lists.
If she does laundry lists, she does not do UX but I do not care, because she does not consult this list. The solution has an important chance of being late, exceeding the budget and ultimately being useless.
On the other hand, if the BA is writing US or CUs, then there is a chance that she will do so Interaction Design.
It's her responsibility, but she can share it with a guy from UX if she's available.
It is in the writing of the user interaction steps against the system that the interaction is defined, better by the UC than by the US (but it can use the two).

interaction design

It is of paramount importance for the application (or web page, or other) to be usable.
Later, the visual design will surely add its share, but in the beginning, the application must have a relatively good interaction design so that users do not get lost in the meandering actions required for it. use with efficiency, effectiveness and satisfaction. .
This is so important because the interaction bloopers found later during user testing will not be fixed because it's so expensiveand no one will have the courage to tell the investor the extra time and money it would take.
The BA is responsible for the design of the interactions because initially she talked to the users, showed them how they work and understood their goals and needs.

during the development phases

The mission of the BA is to ensure that what programmers are programming and what designers design is their vision of the solution.
In addition, if they run an agile process (such as the usual Scrum), they will work full-time writing user stories so that development teams do not starve (out of backlog) and a lot of tasks.
But I mention the US thing because it should convey the design of the interaction or let the programmers get results at the Dilbert.

usability vs UX

For the experience to be beneficial for the user, the user interface must first be usable. That's what the BA has to provide.
After that, it can become an "experience", but if the usability is not good, it will never be such a good experience for the user to feel what we wanted.