Database

CREATE TABLE ObjectOne
(
  Id   int,           -- primary key
  ...                 -- more fields
)
CREATE TABLE ObjectOneProperties
(
  ObjectOneId         int,   -- primary key, foreign key to the object one
  ObjectPropertiesId  int,   -- primary key, foreign key to the properties
)

CREATE TABLE ObjectTwo
(
  Id   int,           -- primary key
  ...                 -- more fields
)
CREATE TABLE ObjectTwoProperties
(
  ObjectTwoId         int,   -- primary key, foreign key to the object two
  ObjectPropertiesId  int,   -- primary key, foreign key to the properties
)

CREATE TABLE ObjectProperties
(
  Id              int,          -- primary key
  PropertyType    varchar(255)  -- property business type
  ???                           -- property value ? foreign key(s) ?
)

CREATE TABLE PropertyValues
(
  Id             int,          -- primary key
  ValueInt       int,          -- value as int
  ValueText      varchar(x),   -- value as text
  ValuedateTime  datetime,     -- value as datetime
  ...                          -- all other value types
)

CREATE TABLE PropertyIntValues
(
  Id       int,                -- primary key
  Value    int                 -- value as int
)
CREATE TABLE PropertyTextValues
(
  Id     int,                  -- primary key
  Value  varchar(x)            -- value as text
)
CREATE TABLE PropertyDateTimeValues
(
  Id     int,                  -- primary key
  Value  datetime              -- value as datetime
)
CREATE TABLE PropertyXxxxValues  -- for any other value types
(
  Id     int,                  -- primary key
  Value  xxx                   -- value as xxx
)