There is nothing in law that governs the break up of salary structure.
You are free to set up any structure you wish, subject to certain legal requirements.
First is that basic + da must be more than minimum wages
Second, in Maharashtra, you need to give 5% HRA (compulsory)
Some other states have such requirements. Like in jharkhand, those working in Jamshedpur are entitled to medical allowance of rs. 0.50 per day
Income tax allows tax free conveyance allowance of rs. 800 per month. So giving a conveyance allowance if 800 in the salary structure is tax beneficial to employees. Similar rules are available regarding HRA and some other allowances under the tax laws.
However, while these are tax beneficial, nothing in law requires you to give the same.
Normally, the salary in private companies has a balancing head called 'Miscellaneous/ Special Allowance'.The remaining sub-heads are Basic, HRA (which is up to 50% of Basic), EPF (company contribution), Medical Allowance (Rs 15 K per annum, tax free), ESI (company share, as applicable), Conveyance Allowance (Rs 9600 per annum, tax free). If an employee's total salary is Rs XXX and the Basic + Allowances (mentioned above) are Rs YYY' then the Miscellaneous/ Special Allowance will be: (Rs XXX - Rs YYY).
You may observe that Miscellaneous/ Special Allowance can take into account all types of allowances such as: Qualification Allowance, Cost of living allowance, Car/ Fuel Allowance, Mobile Allowance, Lunch Allowance, Night working Allowance etc.... Since all income (including perks) is taxable these days, clubbing various types of allowance under one sub-head makes the salary administration easy.
Evenif you pay other allowances,employee's basic & DA only will be taken in to account for gratuity purposes.If you give a certain percentage of basic as DA,that has to be revised quarterly with the %age change in AICPI. Perks and Allowances you pay add up to the salary and are taxable. There is no legal hurdle in defining the salary structure as per company's convenience. Only thing is that it should not fall below the minimum wage notified for different categories of employees. Thank You.