12.3.1 HII Database Protocol and HII String Protocol

Use the database protocol to submit the package of strings, fonts, forms, and so on, to the HII database. It is the most important of the HII protocols. Because the package is created at build time, and most of the package does not change, the driver does not have to call much later. This can significantly speed up boot time.
The strings protocol allows the general purpose forms to adapt to the configuration of a specific platform. This includes configuration information typed in by the user. The forms themselves are created by the VFR during build.
Basically, the string and database protocols facilitate database and string management. The browser simply gets things out of the database after the driver uses the set functions to put data into the database. The browser doesn't need to know how to parse the database or even know how strings are stored; it needs to know only how to parse the forms.
The EDK II provides a library, in the MdeModulePkg, called HiiLib that provides helper functions to simplify the use of the HII Database and HII String protocols. It also provides services to dynamically generate forms. HII Database Protocol

HII data is contained in HII packages. For example, A driver might have a string package, a form package, and a small font package. HII supports package lists as a way to combine HII packages to create a single data structure for all the user interface HII data necessary for the driver. Rather than requiring the driver to split the packs up to, for example, provide the string pack to the string protocol and the font pack to the font protocol, the HII Database Protocol consumes the entire package list and portions it out to the various parts of the HII database. The package list format is described in the Human Interface Infrastructure Overview chapter of the UEFI Specification.
When a package list is submitted to the database (via NewPackageList), an ID, known as an HII handle, is associated with the data. This handle is required to manipulate the pack list's data to ensure uniqueness. For example, if two drivers submit string packs to the database, each have a string with an ID of 1 but they are different. The handle indicates which string with an ID of 1 to access.
One parameter to NewPackageList deserves special attention: DriverHandle. The driver handle indicates the handle on which the driver has put an instance of the CONFIGURATION_ACCESS_PROTOCOL. This protocol is used to obtain ("extract") the current configuration of a driver and to provide new configurations to it.
UpdatePackageList allows a driver to associate more than one package list with the same handle. This may simplify complex configurations by splitting the package into a common piece and additional configurations depending upon the cards SKU.
The Database protocol also supports methods to extract pieces from the database up to and including the entire database as well as ListPackageLists and ExportPackageLists. These functions are rarely useful for a driver but are the mechanisms by which the system places the HII data into the system table and also how the Setup browser obtains the data used to present its screens. The database protocol also supports notification functions for consumers of database data so they can determine if new packages have been added or existing ones removed.
Questions commonly asked include: Why are there individual protocols for some package types? Why isn't there a single protocol? The main reason is that the number of functions required became unwieldy. A secondary reason is that, for some smaller implementations, subsets of HII could be implemented. In reality this has not occurred.
The keyboard packages were judged as being simple enough to leave in the database protocol. Keyboards are abstracted using a data structure per key. Each data structure defines the key code to which the data structure refers, as well as the unmodified Unicode weight and the weights when modified with Shift, Alt, and Shift + Alt. Only the keys that vary from the standard US English layout need be specified. Certain keys, such as NumLock, may also be assigned special functions. HII String Protocol

The String Protocol consumes string packs. It also allows manipulation of strings already in the database, even if they were submitted via the database protocol.
It is quite common for a driver to need to manipulate certain strings when its data is in the HII database. Consider the case of a media card with attached mass storage devices. When the driver for the media card is created, the identification data of the mass storage devices attached aren't known. That data is derived when the card's driver is invoked, generally at Start().
If the driver is to provide the mass storage device types to the setup browser, it is common to allocate empty strings so the build allocates string IDs to the strings. The driver can then parse the string pack to modify strings updating them with the drive id data itself and then submit the string pack. This is complex and tedious because the string packs are stored to be space efficient, not to be easily accessible. The String protocol already knows how to parse the string pack, however, and does provide methods to modify strings by ID. This makes the job of updating strings for dynamically derived data an easy one. Simply submit the string packs to the database, then modify the few strings that change dynamically. Blank strings can be checked for in IFR so empty channels don't have to be displayed. Adding data to the HII database at boot time

There is more than one way to add information to the database. A crude way of adding information to the HII database is by using individual protocols to specify the fonts, strings, and forms. A better way is to use the HII Database Protocol. This protocol provide services to register the strings pack, fonts pack, forms pack, and so on, all at once. Because most of the package is static data, the driver does not have to do much work later during boot.
Note: If the VFR compiler is used as part of the build, the package created may be published with this protocol.
Also, note that the database is not complete at build time. The driver cannot know all the data it needs about the end-user's specific system hardware or other devices connected to the hardware. For example, the driver can't know a specific platform's MAC address at build time, which specific mass storage devices are attached via SCSI, each mass storage device's version information, and so on. That type of information is acquired during setup. During setup or boot, the package for the HII database must be updated.
Although data may be modified before being submitted to the database, that process is both difficult and convoluted. Use the SetString() function in the HII String Protocol instead.
For configurable data, or for data not available at build time, use a question mark in the package for each of the blank fields. During boot, the driver requests that information. Use the set string functionality of the HII String Protocol to specify the ID of the new package list and update the database with the new string from the build file.
Note: If driver A creates a package list for the database, and another driver B creates another package list for the database, driver A's string #12 is not the same as driver B's string #12. Update the database via the byte offset of a configurable field

To modify a form after build-time, include a comment line (a macro for the VFR compiler) in the form's source code. The comment line does not generate code in the form. It simply indicates the byte offset of the value which does change the platformspecific information. The driver does not need to know how to parse the whole form to find that value. Instead, a driver can use the offset to find out where to edit the form.
Take the example of a SCSI driver with 2 drives specified as the default. In this example, the end-user platform actually has 3 drives. The driver searches for the appropriate comment to find the offset and the compiler tells the driver that the description of the logical unit is at line 437 The driver goes to that location, adds new forms data for the third drive and "slides" the rest of the configuration forms down. Essentially, new data is inserted into a newly created hole. Because the Internal Forms Language (IFR) is decision-independent, there are no fixed addresses in the code so data may be moved from one location to another relatively easily. The IFR also uses names for references, not pointers. For example, if 20 bytes of data need to be added at location 437, the 20 bytes can be copied into the new form.
Note: The driver can do a get operation on the whole form or on just the string. The driver can do a get operation on the string because it uses the existing infrastructure (the platform's browser and other tools), which already know how to parse the database to find the appropriate data. Using strings to create forms as-needed

Use strings to create forms as needed. For example, most of the time, a SCSI has only 2 drives, but could have up to 8 Instead of creating a static form with 8 fields, and only 2 filled at boot time, a form with the 2 required fields can be created dynamically. The other 6 unused fields would not be displayed until they are actually needed. Using strings to modify forms

In general, about 80% of any given form is static and common across the system's hardware. The other 20% is specific to that platform.
When adding information after build, it is sometimes easier to simply update a form. Other times it's easier to create a new form and turn it in. In general, a new form should be created if 70-80% of the information is new or has changed.
The VFR programming language explains how to work with forms and includes tips and suggestions for modifying forms. HII Database Protocol with Export Package List

The HII Database Protocol provides a service to export all registered packages into an Export Package List. This includes packages registered by all UEFI Drivers. The Export Package List is not typically used by UEFI Drivers themselves. Instead, its purpose is to provide a single interface for external entities to extract the data needed to configure the system remotely.
Note: Programs that perform remote configuration do not have access to callbacks so questions related to callbacks are not visible remotely. Requests to read and write configuration data are routed to HII Config Access Protocol instances.